safe to say, would include illustrations from other branches of science, as well as my own.

--

But - and here I ask pardon if I speak of myself I have been led to review the labors of other searchers from this standpoint, because I had first learned, out of personal experience, that the most painstaking care was no guaranty of final accuracy; that to labor in the search for a truth with such endless pains as a man might bestow if his own salvation were in question did not necessarily bring the truth; and because, seeking to see whether this were the lot of other and greater men, I have found that it was, and that, though no one was altogether forsaken of the truth he sought (or, on the whole review of his life as a seeker, but might believe he had advanced her cause), yet there was no criterion by which it could be told at the time, whether, when after long waiting there came in view what seemed once more her beautiful face, it might not prove, after all, the mockery of error; and probably the appeal might be made to the experience of many investigators here with the question, Is it not so?"

What then? Shall we admit that truth is only to be surely found under the guidance of an infallible church? If there be such a church, yes! Let us, however, remember that the church of science is not such a one, and be ready to face all the consequences of the knowledge that her truths are put forward by her as provisional only, and that her most faithful children are welcome to disprove them.

What then, again? Shall we say that the knowledge of truth is not advancing? It is advancing, and never so fast as to-day; but the steps of its advance are set on past errors, and the new truths become such stepping-stones in turn.

To say that what are truths to one generation are errors to the next, or that truth and error are but different aspects of the same thing to our poor human nature, may be to utter truisms; but truisms which one has verified for one's self out of a personal experience are apt to have a special value to the owner; and these lead, at any rate, to the natural question, "Where is, then, the evidence that we are advancing in reality, and not in our own imagination?"

There are many here who will no doubt heartily subscribe to the belief that there is no absolute criterion of truth for the individual, and admit that there is no positive guaranty that we, with this whole generation of scientific men, may not, like our predecessors, at times go the wrong way in a body, yet who believe as certainly that science as a whole, and this branch of it in particular, is advancing with hitherto unknown rapidity. In asking to be included in this number, let me add that to me the criterion of this advance is not in any ratiocination, not in any a priori truth, still less in the dictum of any authority, but in the undoubted observation that our doctrine of radiant energy is reaching out over nature in every direction, and proving itself by the fact that through its aid nature obeys us more and more; proving itself by such material evidence as is found in the practical applications of the doctrine, in the triumphs of modern photography, in the electric lights in our streets, and in a thousand ways which I will not pause to enumerate.

And here I might end, hoping that there may be some lessons for us in the history of what has been said. I will venture to ask the attention to one more, perhaps a minor one, but of a practical character. It is that in these days, when the advantage of organization is so fully recognized, when there is a well-founded hope that by co-operation among scientific men knowledge may be more rapidly increased, and when in the great scientific departments of government and elsewhere there is a tendency to the formation of the divisions of a sort of scientific army, a tendency which may be most beneficially guided, that at such a time we should yet remember, that, however rapidly science changes, human nature remains much the same; and (while we are uttering truisms) let us venture to say that there is a very great deal of this human nature even in the scientific man, whose best type is one nearly as unchanging as this nature itself, and one which cannot always advantageously be remodelled into a piece of even the most refined bureaucratic mechanism, but will work effectively only in certain ways, and not always at the word of command, nor always best in regiments, nor always best even under the best of discipline.

Finally, if I were asked what I thought were the next great steps to be taken in the study of radiant heat, I should feel unwilling to at

tempt to look more than a very little way in advance. Immediately before us, however, there is one great problem waiting solution. I mean the relation between temperature and radiation; for we know almost nothing of this, where knowledge would give new insight into almost every operation of nature, nearly every one of which is accompanied by the radiation or reception of heat, and would enable us to answer inquiries now put to physicists in vain by every department of science, from that of the naturalist as to the enigma of the brief radiation of the glow-worm, to that of the geologist who asks as to the number of million years required for the cooling of a world.

When, however, we begin to go beyond the points which seem, like this, to invite our very next steps in advance, we cannot venture to prophesy; for we can hardly discriminate among the unlimited possibilities which seem to open before a branch of knowledge which deals especially with that radiant energy which sustains, with our own being, that of all animated nature, of which humanity is but a part. If there be any students of nature here, who, feeling drawn to labor in this great field of hers, still doubt whether there is yet room, surely it may be said to them, “Yes, just as much room as ever, as much room as the whole earth offered to the first man;" for that field is simply unbounded. and every thing that has been done in the past is, I believe, as nothing to what remains before us.

The days of hardest trial and incessant bewildering error in which your elders have wrought seem over. You "in happier ages born," you of the younger and the coming race, who have a mind to enter in and possess it, may, as the last word here, be bidden to indulge in an equally unbounded hope.

A PLEA FOR LIGHT-WAVES.1

IT is no doubt universally conceded that no era in the world's history has ever seen such immense and rapid strides in the practical applications of science as that in which it is our good fortune to live. Especially true is this of the wonderful achievements in the employment of electricity for almost every imaginable purpose. Hardly a problem suggests itself to the fertile mind of the inventor or investigator without suggesting or demanding the application of electricity to its solution.

If we except the exquisite results obtained in the manufacture and use of diffraction gratings, and the very important work accomplished by the bolometer (a purely electrical invention, by the way), it may well be questioned whether, within the last twenty years, there has been a single epoch-making discovery or invention either in theoretical optics or in its applications.

It is mainly with a view of attempting to interest brother physicists and investigators in this to me most beautiful and fascinating of all branches of physical inquiry, that I venture to present a limited number of problems, and I think promising fields for investigation, in light, together with some crude and tentative suggestions as to their solution.

The investigations here proposed all depend upon the phenomenon of interference of light-waves. In a certain sense all lightproblems may be included in this category, but those to which I wish to draw your attention are specially those in which a series of light-waves has been divided into two pencils which re-unite in such a way as to produce the well-known phenomenon of interference fringes.

The apparatus by which this is effected is known by the inconvenient and somewhat inappropriate name of 'interferential refractometer.' As the instrument which I had the honor of describing to the section at the last meeting is simple in construction, and has already proved its value in several experiments already completed and in the preliminary work of others now under way, I may be permitted to recall the chief points of its construction and theory. A beam of light falls on the front surface of a plane parallel piece of optical glass at any angle, usually forty-five degrees, - part being reflected, and part transmitted. The reflected portion is returned by a plane mirror, normal to its path, back through the inclined plate. The second or transmitted portion is also returned by a plane mirror, and is in part reflected by the inclined plate,

1 Abstract of an address before the Section of Physics of the American Association for the Advancement of Science, at Cleveland, O., Aug. 15-22, 1888, by Albert A. Michelson, vice-president of the section.

thus coinciding with the transmitted part of the first pencil; and the two pencils are thus brought to interfere.' A little consideration will show that this arrangement is exactly equivalent to an air-film or plate between two plane surfaces. The interference phenomena are therefore the same as for such an air-plate. If the virtual distance between the plane surfaces is small, white light may be employed, and we have then colored fringes like Newton's rings or the colors of a soap-film. If the distance exceeds a few wave-lengths, monochromatic light must be employed. We may confine our attention to the case of two parallel surfaces. Here it can readily be shown that the fringes are concentric circles, the common axis of the rings being the normal passing through the optical centre of the eye or telescope. Further, they are most distinct when the eye or the telescope is focused for parallel rays. In any other case we are troubled with the same perplexing changes of form and position of the fringes as already noted.

If, now, one of the mirrors have a motion normal to its surface, the interference rings expand or contract; and, by counting the fringes as they appear or disappear in the centre, we have a means of laying off any given distance in wave-lengths.

Should this work of connecting the arbitrary standard of length - the yard or the metre — with the unalterable length of a light-wave prove as feasible as it is hoped, a next step would be to furnish a standard of mass based upon the same unit.

Suppose a cube, ten centimetres on a side, with surfaces as nearly plane and parallel as possible. Next suppose a testing-instrument made of two parallel pieces of glass, whose inner surfaces are slightly farther apart than an edge of the cube. The parallel-, ism and the distance of these surfaces can be verified to a twentieth of a wave. Now apply this testing-instrument to the three pairs of surfaces of the cube, and determine their form, parallelism, and distance to the same degree of accuracy. We have thus the means of measuring the volume of a cubic decimetre with an error less than one part in a million.

It does not seem extravagant to say that by some such plan as this we may obtain a standard kilogram which will be related to the standard of length with a degree of approximation far exceeding that of the present standard. The apparatus can also be used in the manufacture of plane surfaces, and in the measurement of co-efficients of expansion.

For all measurements of refraction and dispersion, for solids and liquids as well as for gases, and in the determination of the wave-length of standard lines, the accuracy of the measurement of absolute wave-lengths will depend on the accuracy with which the fixed distance can be compared with the standard metre; and this may be estimated as one part in two million.

The results of the remarkable work of Rowland do not claim a much greater degree of accuracy than one part in half a million for relative determinations; while the elaborate research of Bell on absolute wave-lengths claims but one in two hundred thousand. It may possibly help to realize the very considerable superiority of this instrument over the grating at any rate, for the class of work in question — if I recall to your attention the fact that by its means it has been possible to show that the red line of hydrogen is a very close double.

Closely connected with the preceding investigations is the study of the effect of the temperature, thickness, and density of the source on the composition of the radiations, as shown by the symmetrical or unsymmetrical broadening of the spectral lines, and the consequent shifting of their mean position. This question has quite recently been taken up by H. Ebert, and the results he has already obtained are very promising. Ebert has established two conclusions, which, if verified, are of the greatest importance: namely, first, that the chief factor in the broadening of the spectral lines is the increase in density of the radiating body; second, that the broadening, in all the cases examined, is unsymmetrical, causing a displacement of the line toward the red end of the spectrum. The importance of these conclusions, in their relation to the proper motions of the heavenly bodies and their physical condition, can hardly be overestimated. The value of results of this kind would, however, be much enhanced if it were possible to find a quantitative relation 1 A second plane parallel plate of the same thickness and inclination is placed (for compensation) in the path of the first pencil.

between the density of the radiating substance and the nature of its radiations. In the case of hydrogen enclosed in a vacuum tube this could readily be accomplished. It may, however, be objected that it would be difficult in this case to separate the effects of increased density from those due to the consequent increase in the temperature of the spark. The problem of the temperature of the electric discharge in rarefied gases is one which has not yet been solved. In fact, it may seriously be questioned whether in this case temperature has any thing to do with the accompanying phenomena of light; and it appears to me much more reasonable to suppose that the vibratory motion of the molecules is not produced by collisions at all, but rather by the sudden release of tension in the surrounding ether.

THE present volume consists of a number of extracts from Kant's principal works, -The Critique of Pure Reason,' 'The Metaphysic of Morality,' The Critique of Practical Reason,' and 'The Critique of Judgment,' — and is intended for the use of teachers of philosophy. Undoubtedly the study of Kant is the best introduction into modern philosophy, and a powerful means of guarding students from falling into a shallow materialism or positivism. The extracts are well selected, and the difficult task of rendering Kant into intelligible English without altering the character of his style too much has been skilfully solved. The book is an enlarged edition of the author's Extracts from Kant's Writings, which was originally printed for the use of his own students. Professor Watson says that he found by experience the results obtained by means of lectures on philosophy very unsatisfactory, as the students did not learn to think for themselves: therefore he adopted the plan of supplementing his lectures by the study of the writings of various philosophers. This is the same method which is so successfully followed at German universities in what are called seminaries.' The teacher who will take this course will find Watson's book very useful and convenient, as it contains the salient points of Kant's philosophy.

Latin Accidence and Exercises. By W. WELCH and C. G. DUFFIELD. London and New York, Macmillan. 24°. 40 cents. THIS book is intended as an introduction to Macmillan's Elementary Classics.' The principles on which the authors' plan is based are a thorough and accurate mastery of the elements of the Latin language, and the putting into intelligent practice at once what has been learned, thus avoiding as much rote-work as possible. The examples have been taken largely from the Public Schools Latin Primer,' as the latter is most widely used in the higher forms. The authors do not deem it desirable that beginners should learn the conjunctive mood, which, for this reason, has been added in small type at the end of the Accidence.' The book is intended to be mastered in two terms.

Elementary School Atlas. By J. BARTHOLOMEW. Macmillan. 8°. 30 cents.

London,

THE publication under review belongs to Macmillan's Geographical Series, edited by A. Geikie, who promoted the interests of teaching geography so well by his well-known essay on this subject. As might be expected, the atlas represents a great improvement upon the ordinary English elementary school-maps, the material which is embodied in the maps being carefully selected, and the abominable relief-plate printing being at last discarded, a clear lithograph taking its place. The atlas contains twenty-four maps or plates. The first shows a number of hemispheres: the northern and southern (land and water) and the European and South American. We would gladly miss the last, as it is intended only to show the central position of Europe. The second map is named Europe, illustrating Geographic Terms.' This map must be considered a failure, as it attempts the explanation of geographic terms, instead of by means of objects, by that of a highly and wrongly generalized map. The following plate, which illustrates the mapping of a landscape and the influence of reduction, ought

to precede the former, and we believe greater care in its technical execution would have been desirable. As the map is intended to explain the meaning of hill-shading, the view of the hills and the map ought to be clear, and it ought to be possible to compare them down to minute details. The fourth plate explains the system of meridians and parallels and the curvature of the earth's surface. The rest of the maps are well selected, and do not call for any special comment. The maps of the British Isles are very good. We think, however, that a hypsometric map like No. 11 is of no great value for educational purposes, as contour-lines, unaided by hill-shading, do not convey to the child a good idea of the physical features of a country. Considered as a whole, the atlas must be commended as a great improvement upon the ordinary school atlas.

NOTES AND NEWS.

THE United States Fish Commission is undertaking an extensive series of explorations of the fish fauna of the rivers of the Alleghany region. The work is in charge of Prof. D. S. Jordan, assisted by Prof. P. P. Jenkins, Prof. B. W. Evermann, and Mr. Barton A. Bean. The basins of the James, Kanawha, Roanoke, Holston, French Broad, Yadkin, and Catawba will be included in the work of the present summer. Similar explorations of the smaller lakes of Michigan are under direction of Mr. Charles H. Bollman.

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- The fourth article in the Railway Series now appearing in Scribner's Magazine will be contributed to the September number by Gen. Horace Porter, who writes of Railway Passenger Travel.' The Record of a Human Soul' is the title of an anonymous little book to be published shortly by Longmans, Green, & Co. It is the honest account of the struggle of a sceptic, who ardently but unavailingly desired to believe, from the coming of the doubt until the hour when the doubter at last sees a light in heaven. It is introspective and subtle, but not morbid; its language is simple and direct; and the record is likely to be useful to not a few who have only the honest doubt in which there may be more faith than in half the creeds.

The Canadian Institute, Toronto, Ont., is desirous of collecting, and incorporating in its Proceedings, reliable data respecting the political and social institutions, the customs, ceremonies, beliefs, pursuits, modes of living, habit, exchange, and the devolution of property and office, which obtain among the Indian peoples of the Dominion. It feels that this department of research has not been so fully cultivated in Canada as its importance demands, fears that the opportunity of gathering and carefully testing the necessary facts may with the advancing tide of European civilization soon pass away, and is of opinion that much light may be cast upon the genesis and growth of government as well as upon legal, sociological, and economic thought by an accurate study of the Indian tribes in their existing conditions and organizations. Contributions to the philology of the Indian tongues, and additions to their folk or myth lore, will be welcomed as heretofore. At the same time the institute begs leave, without desiring to contract the field of observation, to direct attention to the sociological matters.

46

A new process for protecting iron against corrosion, now employed by a company at Port Chester, N.Y., is said to give satsfactory results. The company is now manufacturing sanitary soilpipes treated by this method, which is described by Mr. H. Haupt as follows: After the pipes have been lowered into the retorts by means of a traveller, the retorts are closed for about fifteen minutes until the contents are heated to the proper temperature. Steam from a boiler at sixty pounds pressure is then introduced into the superheater, which it traverses, and from which it escapes at the temperature of the iron, upon which it acts for about one hour. A measured quantity of some hydrocarbon is then admitted with a jet of steam, followed again by a fixing bath of superheated steam, which completes the process." Professor Gesner, the director of the works, says there is no pressure in the retort, and that there are no free explosive gases. The water-seals attached to the retorts show only slight oscillations, but not an inch of pressure; and when the covers are removed and air admitted there is no explosion, as there always is when free hydrogen or carbonic oxide is present. The absence

of pressure and of explosive gases is a proof that all the operations have been so nicely regulated as regards material used, quantity, and time of application, that a perfect absorption and union of the carbon, oxygen, and hydrogen with the iron has been effected. The protection thus afforded to the iron is not a mere coating, like paint, but is said to be an actual conversion, to a greater or less. depth, into a new material. When properly treated, this material does not seem to be detachable by pounding, bending, hammering, rolling, or heating. The pipes treated at Port Chester have been immersed in baths of dilute sulphuric acid and exposed to the salt air for weeks without change, while untreated pipes were quickly covered with red oxide, or with sulphate of iron.

LETTERS TO THE EDITOR.

Re-appearance of Song-Birds.

THE appearance of birds is always quite irregular, so far as numbers are concerned, with the possible exception of one or two varieties like the migratory thrush. We will find in any locality that the oriole is very plentiful for a few years, and then comparatively scarce for a few years. This cannot be mistaken by those on whose gardens he makes his inroads. The absence of grossbeaks and then their great abundance is equally marked. So of nearly all familiar birds. The cause is probably that they range over a large territory, and select different nesting-centres. It is well known that pigeons will cover the sky for two or three springs, moving to a camp in the farther north, and then for years not a pigeon be seen. I believe my catbirds alone have so taken to me that I can always count on their familiar forms and delicious

notes.

The extraordinary abundance of song-birds is no doubt a simple coincidence or accidental agreement of action on the part of several species. In my own grounds I do not see any such unusual migration; for the reason, probably, that I have for many years so protected and fed them, that it is a paradise for birds. Yet it is true that several sorts of birds are on the increase here; owing, possibly, to finding their quarters disturbed elsewhere. The line of migration can be much more easily swerved than the ponderous and slow movements of animals. I think you may be sure that the abundance in some quarters is balanced by the deficit in other quarters. New influences constantly arise, affecting the peace and content of birds. I have all summer been fighting a band of pseudo-scientists; that is, boys who carry papers permitting them to shoot our birds to make collections for so-called scientific purposes. Before the law to protect our song-birds, no decent young man would prowl about near our residences to shoot the pets. But now they are 'scientists;' and we have no rights to be considered. They crack their guns under our very noses. But I have vowed to have a lawsuit with every budding Audubon that comes this way, and am at present ahead.

Now, here is a law that works not at the muzzle, but the but.. Its effect is to scatter our birds in their favorite haunts. My grounds cover nine acres only, but several neighbors are in full accord; and there are full fifty acres of flowers, hedges, and fruit where the song-birds are wonderfully abundant. But how long would they remain with us if one after another fell victims the moment they flew outside our lines? Another year we should lament the absence of our birds, and somewhere else people would E. P. POWELL. rejoice in their superabundance. Clinton, N.Y., Aug. 7.

The Physical Aspect of the Planet Mars. THERE has been so much said of late, in the newspapers and elsewhere, in regard to the parallel canals of Mars, that perhaps a brief discussion of the facts observed in regard to them may be of interest. And first of all it may be remarked, that, of all the different methods of accounting for the appearances observed, perhaps the least probable is that they are water-canals.

Let us see what are the facts in the case. According to the observations of Schiaparelli (Reale Accademia dei Lincei 1881 and 1886) they lie almost entirely between 50° north and south latitude (that is, in the torrid and warmer portions of the temperate zones), and extend across the continent from the northern to the southern

ocean. They are in general two or three thousand miles in length, though sometimes much longer, by from perhaps thirty to one hundred and fifty miles in breadth. They are generally arranged in pairs two or three hundred miles apart, drawn on the arcs of great circles, and so exactly parallel that usually no deviation can be detected. They run in all directions, but there are about a dozen points which seem marked as special centres from which they radiate. Thus ten start from the Trivium Charontis as a centre, and eight from the Lacus Phoenicis. They cut up the continental surface of the planet so that there is no spot more than four hundred miles distant from one of these markings. They are usually so fine that no color can be assigned to them, and they can be merely spoken of as dark lines; but in a few instances where they broaden out, as in the Lyrtis Major (if this conspicuous marking can be considered one of them), they are decidedly darker than the oceans, and of a grayish or perhaps greenish tint.

Of a well-defined canal called by Schiaparelli, Hades, M. Perrotin (Annales de l'Observ. de Nice, c. 58) remarks, "Since our first observations, the canal LN has suffered a considerable change: we can distinguish it no longer save to a feeble extent on the side marked N. Though drawn on the map of M. Schiaparelli of 1882, this canal does not exist on that of 1879. Our observations, then, not only confirm the changes already stated, but they show further that these changes may be produced in a short period of time." Other evidences of change have since been observed. It is thought that a large portion of the red region known as Libya had changed to green, and afterwards in part back to red. But the latest evidence of change, according to M. Perrotin (Comptes Rendus, cvi. 1718, and cvii. 161), is the carrying of several of the so-called 'canals' across the northern ocean up to the polar ice-cap. If the observation is correct, it is clear that either the ocean is not an ocean, or the canals are not canals. If the observation were confirmed, I should be inclined to deny both propositions. Indeed, the northern ocean as represented by M. Perrotin at this point is but little more than an enlarged canal, while M. Schiaparelli does not indicate it at all upon his maps.

The latter has thought that many of these canals appear only for short time, and then disappear again; and some of them he has only seen shortly after the passage of the vernal equinox on Mars, and thinks that there may be some relation between the two.

To every argument as to the inherent improbability of an/ hypothesis made with regard to a remote planet, we may be met by the statement that under different conditions these very things may happen, - a statement easily made, and hard to refute. The best we can do, however, is to reason by means of the laws which we have found to apply in the case of the earth. Certainly no such straight canals could be made here naturally, and, if they were made, they would soon be filled up again. If, on the other hand, the canals were artificial, what could be the use of making them so wide, why arrange them always in duplicate, and why fill certain of them up every year, later to be re-opened? Think of the labor involved in covering over, and then re-opening, a canal, say, sixty miles wide by three thousand miles long, and all in the space of a few weeks. Moreover, in the case of those which are sufficiently wide for us to see distinctly, why should the color be so much darker than that of the neighboring oceans?

Mr. R. A. Proctor has suggested (Monthly Notices Roy. Ast. Soc., xlviii. 307) that the canals are the diffraction-images of rivers produced by mist which hangs over the river-beds. To this suggestion, however, some of the same objections apply as to the other. M. Fizeau's suggestion (Comptes Rendus, cvi. 1759), that the stripes are cracks between huge masses of ice, presents some difficulty in accounting for the red color of the ice; and also, as was pointed out by M. Flammarion (Comptes Rendus, cvii. 19), since the temperature of Mars as indicated by the size of the polar spots, is, if any thing, higher than that of the earth, it is surprising that the ice does not melt.

probable that these particular stripes are really there. M. Perrotin has confirmed the doubling of the stripes previously mapped by M. Schiaparelli: it is therefore quite possible that these are genuine also, although the observation is one of extreme difficulty, requiring the steadiest possible atmospheric conditions. But the statement that a change in the markings has been observed is one that must be received with extreme caution, and, although a most interesting one, must for this very reason be only accepted as proved, when confirmed by observations made with the most powerful telescopes at our disposal, and under the most favorable circumstances.

Starting out from the generally accepted fact that there are stripes upon the planet, we find there are five possible hypotheses to explain their existence. Three, that they are due to water in the vaporous, liquid, or solid condition, we have already noticed. Fourth, we may explain them by supposing them to depend on the color of the rock or soil, and that their shape depends on some peculiar geological formation. We have, to be sure, no such formations upon our globe; but we have something analogous, though on a somewhat smaller scale, upon the moon. There we find numerous long nar

row streaks radiating from the crater Tycho, as also in a lesser degree from some of the other craters. The streaks are perfectly straight, of very light color, and in a few cases we find them arranged parallel to one another.

As to the color of Mars, it is probable that the earth would appear of the same color as seen from a distance, if deprived of its vegetation, owing to the red color of its soil in most parts of the world, particularly in the warmer regions.)

If it can be shown, however, that at certain seasons the stripes on Mars really disappear, through some other cause than that of passing clouds or haze in its own atmosphere, then this hypothesis, like that of the water-canals, must fail.

The fifth and last of the possible explanations is that the stripes are due to differences in vegetation. Whether the stripes indicate vegetation, and the rest is a barren waste, or whether a large proportion of the vegetation of Mars is of a reddish color, as suggested by Lambert among others, and approaches in tint to our coleus and autumn leaves, is a matter of no consequence at present. If it can be shown that the stripes on Mars really change, this will be the hypothesis that we shall be forced to adopt, or, rather, we should say it is the only one left presenting no serious improbabilities.

Let us now review the already ascertained facts with regard to the planet. We are reasonably certain that the surface of Mars is composed of land and water; that it has snow at its poles, and therefore an atmosphere containing clouds. As the snow does not extend over the whole planet, but varies in extent at different times, and what are apparently clouds have been observed in other regions of its surface, it is probable that they likewise have rain. Their temperature cannot be very different from ours, judging by the extent of the snow at the poles, which is rather less in proportion than with us, and has in some instances been known to entirely disappear. Their days are but forty minutes longer than ours; and their seasons, owing to the inclination of the axis of Mars, are practically the same. The most marked difference between the two planets, of which we are certain, is, that, owing to the lesser attraction of Mars, bodies there would weigh but two-fifths as much as with us: a man, for instance, weighing one hundred and sixty pounds here, would weigh but sixty-four pounds upon Mars. All the conditions as far as we can determine, save that their sunlight is somewhat weaker, are as favorable to the growth of organic life there as here.

The spectroscope teaches us that the same elements are found throughout the universe: therefore, if we define vegetable life as consisting of organized structures absorbing carbonic acid and giving out oxygen, it will be seen that the admission that vegetable life exists upon Mars carries with it animal life also as a corollary, or vegetation would soon cease for lack of fresh air.

As Mars is a smaller planet than the earth, and more remote from the sun, it probably reached a suitable temperature to support organic life at an earlier date. The laws of evolution have therefore had sufficient time to develop reasonably highly organized animal as well as vegetable life.

This is as far as we are justified in carrying our hypothesis, unsupported by other facts; but now let us give rein to our fancy for

a moment, and suppose an observer on Mars were to examine the earth with successive increasingly powerful telescopes. The first artificial production that he would probably be able to see would be some of the great grain-fields of our Western States. These he would find of irregular shape, but bounded more or less by straight lines. They would appear of a greenish color, not very different from that of our oceans; and he would find them subject to great changes at certain seasons, sometimes perhaps entirely disappearing from sight, when of the same tint as the surrounding country. In fact, if an observer were placed on Mars, and furnished with one of our more powerful telescopes, he would see just about as much of our grain-fields as we do of their stripes, and the only noticeable difference between the two would lie in their shape. Indeed, assuming an artificial origin, it would be easy to frame hypotheses accounting for their form, dependent upon the peculiar conformation of the land surface of Mars, or for their radiating in several instances from particular points as centres.

But to return to our hypothesis, that the stripes are of vegetable origin. If it is correct, there is one test to which it must submit. If a change is noted in a given stripe, this change should be in general more or less progressive from the equator towards the poles, or vice versa. I say in general, because it is not probable that the same kind of vegetation would exist all the way from the equator to 50° north or south latitude, nor would it be the same in all stripes having the same latitude. Moreover, in the stripes running east and west, or in those situated near the equator, successive changes would not usually be noticeable. Stripes containing the same kind of vegetation should be similarly affected. Now, in the stripe known as Hades, previously referred to, this very phenomenon was observed. Hades runs in a direction nearly north and south, and extends from latitude 20° to 45° north. The observation in question was made about two and a half of our months after the passage of the northern solstice on Mars. It was therefore in the latter part of their summer when it was found that the southern portion of what had but a few weeks before been a welldefined stripe had completely disappeared.

As an illustration of the formation of a stripe running from the equator towards the pole, let us take the latest observations of M. Perrotin (Comptes Rendus, cvii. 161). According to these observations in the regions as far north as between latitudes 50° and 60°, the stripes did not appear this year until June 4, or four months after the summer solstice. Unfortunately, Mars is now getting so near the sun that it will be probably impracticable to determine the date of their disappearance, should they be found later to have vanished. WM. H. PICKERING.

Observatory, Cambridge, Mass., Aug. 9.

The Philippine Islands.

MR. WALLACE, in his great work, 'The Geographical Distribution of Animals,' divides the Oriental or Indian region of Mr. Sclater into four sub-regions, of which Java, Sumatra, Malacca, Borneo, and the Philippine Islands form one, which he calls the Indo-Malayan. In his discussion of the Indo-Malayan sub-region, Mr. Wallace recognizes several subdivisions of it, and treats of the Philippine group as one of the most important of these. Though acknowledging the existence of divisions of his sub-regions, he failed to give them technical names, as at that time uncalled for. The purpose of this paper is to show that the Philippines themselves are separated into several distinct zoological divisions; and it therefore seems necessary, for their study, to give technical names to the primary and secondary divisions of the already recognized sub-regions. The terms province' and 'sub-province' seem least objectionable, and will be used here; the Philippine Islands thus forming one of the provinces of the Indo-Malayan sub-region, and the divisions of the group itself sub-provinces.

The zoological province of the Philippines is co-extensive with the political division of the same name, with the exception, perhaps, of the islands of Sulu and Tawi Tawi, which lie between the Philippines and Borneo, but are claimed by the Spanish.

The sub-provinces proposed are, first, the northern Philippines, consisting of Luzon, Marinduque, and a number of other small islands about Luzon; second, Mindoro; third, the central Philip

pines, made up of the islands of Panay, Guimaras, Negros, Cebu, Bojol, and Masbate; fourth, the eastern Philippines, comprising the islands of Samar and Leite; fifth, the southern Philippines, embracing the great island of Mindanao, with Basilan; and, sixth, the western Philippines, consisting of the islands of Paragua or Palawan, and Balabac.

The geographical positions of these sub-provinces are fortunately such that these simple names show their relation to each other very closely, as may be seen by consulting a map of the archipelago.

Of these sub-provinces, the western Philippines, made up of Paragua and Balabac, and perhaps the Calamianes, is of most importance, its animal life being much more closely allied to that of Borneo than that of any other sub-province of the group. This is especially noticeable in its mammals, of which it possesses, in common with Borneo, the genera Tragulus, Tupaia, and Manis, which are apparently absent from the rest of the archipelago. Of Bornean genera of birds not found elsewhere in the group, Jora, Criniger, Polyphetron, Tiga, and Batrachostomus are examples The sub-province has evidently received a large part of its fauna from North Borneo, through Balabac, and at a comparatively recent date, and since its separation on the north from the rest of the Philippines, so that these genera have not flown over into Mindoro and Luzon. In addition to these apparently late arrivals from Borneo, the sub-province possesses a large number of peculiarly Philippine birds and mammals, which show that it is an integral part of the province.

The rest of the Philippines would seem to have received its Malayan fauna at another time and by the other way of Sulu and Mindanao. They possess the mammalian genera Galeopithecus, Tarsius, and Cervus, which are apparently wanting to the western sub-province, and the genera Macacus, Sus, Viverra, Paradoxurus, and Sciurus in common with it. Of birds, the genera Loriculus, Cyclopsitta, Buceros, and Penelopides are examples which are more or less generally distributed over the archipelago outside of the western sub-province.

The grounds for dividing the Philippines east of Paragua into sub-provinces are to quite an extent based upon species, and especially upon the existence in each of representative forms of the genera Loriculus, Buceros, Penelopides, Brachiurus, Chrysocolaptes, Dicæum, Cinnyris, etc. The hornbills form, perhaps, the most striking example of this distribution of representative species. Of the eleven species of hornbills collected in the islands, the western sub-province has one, the southern three, the central two, the eastern two, Mindoro one, and the northern two; and we have found no case of a single species occupying more than one subprovince, or of more than one species of a genus in a single subprovince. The genera Chrysocolaptes of woodpeckers is also noticeable, each sub-province possessing its own species, with the exception of Mindoro, which apparently lacks the genus altogether. The genus Loriculus of the parrots is of the same character.

Of other animals than birds, the genus Sciurus of mammals, and Draco, the flying lizards, seem to have representative species in each sub-province, and the land mollusca are probably distributed according to the same plan.

The above examples are a few that come to mind before a careful study of our collections has been made, and they do not by any means represent all the reasons for the conclusions arrived at. These are the result, rather, of the observation of five careful men who have been collecting and studying in the Philippines during the last year. During this time we have visited and collected in fifteen of the islands of the group, and these the largest and most important. I am satisfied that the study of our collections, with the aid of the libraries and collections at home, will only strengthen the conclusions of this paper. It may prove necessary to make the socalled western sub-province of more importance in the arrangement, but the non-existence in nature of exactly equivalent divisions of any kind is well recognized. It is hoped that our work may aid in untangling some of those puzzles in which students of Philippine zoology have found themselves involved, and that it will also add considerably to the sum of knowledge concerning this as yet imperfectly known corner of the earth. J. B. STEERE.

Manila, July 2.