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sandstone; this lava was partially denuded, and buried under a conglomerate composed of its débris, mingled with rhyolitic, trachytic, and granitic material. detritus was also buried under another lava-flow; and this alternating action went on, first with increasing and then with diminishing eruptive activity, until the western sandstones and conglomerates were reached, which were laid down on the last lava-flow. It is probable the lava came from fissure eruptions. Wherever the detritus was deposited on the lava, whether within the trappean belt or on its western side, denudation has taken place, and fragments of the trap (melaphyr and diabase) have been enclosed in the overlying detritus. Unconformability would, of course, thus exist, and the writer has figured such a case; but it is the unconformability that always exists when lava flows on a shore, and is subjected to the denuding action of the waves, and proves nothing regarding the geological age.

The evidence which Irving claims has been ignored, and which he says is "proof absolute that the Keweenawan [copper-bearing rocks] series belongs below the base [Potsdam] of the paleozoic column of the Mississippi" (Geol. Wisc., iii. 23), is principally the finding of a trappean rock at Taylor's Falls, against which rest sandstone and shales holding fragments of the trap and primordial fossils. Excepting the fossils, these are exactly the conditions which are found, and which ought to be found, within the copper-bearing belt, and on its western side; and it proves nothing regarding geological age, but only sequence of time. If such evidence as this is proof absolute' of distinct geological age, then there is proof absolute that there are as many different geological formations in the copper-bearing rocks as there are detrital beds enclosed in the traps, and proof that the last lava-flow of any active volcano, reaching the sea, is separated by a distinct age and immense unconformity' from the detritus deposited upon it before it is hardly cold. Unconformity of itself proves nothing, unless both formations are sedimentary; for an eruptive rock cannot, from the very nature of the case, be conformable, in the true sense, with any thing. The relations that the old basaltic lavas have, according to Irving, to the western sandstone, are exactly what they ought to have from their origin, as shown thirty-three years ago.

Again: according to the Wisconsin geologists, the Taylor's-falls trap is fifteen miles from any other socalled copper-bearing rocks, and may as well be an azoic rock; for similar ones have been collected by the writer in the granite of the Marquette azoic district. If it is referred to the copper rocks on lithological grounds, the same argument could be used to unite with this series a large part of the basaltic traps the world over. The resemblance between them is, in the writer's opinion, that which any two basaltic lava-flows or dikes have wherever they may have been extruded.

The writer has shown that the first trap on the east overflowed and indurated the eastern sandstone; and he collected specimens showing the induration, the trap, and the trappean detritus in the overlying conglomerate. Therefore Irving's statements, that the eastern sandstone unconformably overlies the trap, and that no trappean detritus occurs in the fragmental rocks, are incorrect; and the published evidence was in his hands several years ago. Irving is mistaken when he says that all the geologists who approached the question from the east felt baffled, as the writings of Foster and Whitney, Selwyn, or myself, give no indications of the kind. It may be mentioned, that in 1850 Foster and Whitney showed that a fault

existed along part, at least, of the eastern side of the traps, and that the Bohemian range was a later protrusion. This evidence will explain the apparent unconformity of the traps with the eastern sandstone observed in some places.

For a fuller discussion of the copper-bearing rocks and allied formations, together with the literature down to 1880, the writer would refer to the bulletin of this museum, vol. vii. pp. 1-157. M. E. WADSWORTH.

Museum of comp. zool., Cambridge,

Mass., March 15, 1883.

Domestic ducks that fly abroad like pigeons.

In response to Mr. Storer's note under the above heading (SCIENCE, No. 3), I would state that in my boyhood I lived on a plantation in Liberty County, Ga., on which there were a great many domesticated ducks, both mallards and musk-ducks. Many of these latter belonged to the negroes, and were tended with but little care. Near by the negro village there was a swamp full of large trees, and often covered with water. A considerable portion of the swamp was cleared, and annually planted in rice; but many dead cypress (Taxodium) trees still remained standing. This swamp was a favorite resort for wild ducks of all kinds, especially mallards, teal, and summer ducks (wood-ducks). Many domesticated musk-ducks, especially those belonging to the negroes, flew abroad every morning, remained in the swamp (one to two miles distant) all day, and returned at night. Some of them built their nests and reared their young in the swamp, though they never became thoroughly wild.

I never observed this habit, except in the muskduck. The reason, I think, is plain. In shape, in gait, in flight, and in habits, the musk-duck is very similar to the wood-duck (sponsa). Like the latter, it walks with freer step, it rises, flies, and alights with greater ease and grace, than other species, because the wings are broader and rounder. Like the wood-duck, also, it alights on trees. The dead cypress-trees were a favorite resting-place for the musk-ducks. Like the wood-duck, too, it builds its nest on trees or stumps, and takes down the young when hatched. I have never known the musk-duck to build on the tops of tall cypresses, like the wood-duck, but often on the tops of hollow stumps fifteen to twenty feet high. JOSEPH LECONTE. Berkeley, Cal., March 15.

Apparent attractions and repulsions of small, floating bodies.

To obviate possible misunderstandings, it may be proper for me to make a few remarks in relation to E. H. H.'s' critique (SCIENCE, i., p. 43) on my article (Amer. journ. sc., Dec., 1882) on the above phenomena.

I am to blame for whatever ambiguity attaches to the use of the term 'tension' as applied to the explanation of these phenomena. In one instance (that cited) I inadvertently used the expression 'superior tension' instead of 'superior force.' But inasmuch as in the formal announcement of the capillary principle which is applied to the case in question, and also in the preceding as well as the succeeding context it is very clearly indicated that the effective capillary forces (and not the surface-tension) are regarded as inversely proportional to the radii of curvature of the meniscuses, few physicists will, I trust, be misled by the expression.

He does not admit "that a liquid film tends to draw a solid, to which it is attached, toward the centre

of concavity of the film." The most simple and satisfactory proofs of the relative efficiency, as well as the direction, of the resultant of these capillary forces, are to be found in the well-known contrary movements of small columns of water and of mercury, when introduced into conical capillary glass tubes placed horizontally. In these cases it is evident, that the effective forces are inversely as the radii of curvature of the terminal meniscuses, and are directed toward their respective centres of concavity.

He maintains, that, if the capillary forces were directed toward the centre of concavity of the film, "the tendency of a column of water raised between two floating bodies by surface-tension would be to lift those bodies: similarly, a column of liquid sustained in a fine tube would tend to lift the tube." Simple mechanical considerations are sufficient to show that he is mistaken in supposing that such a result would follow. Indeed, it is obvious that the elastic reaction of the common meniscus, formed when two such floating bodies are brought near to one another, does not tend to lift them: for the vertical component of the capillary forces, directed toward the centre of concavity, is exactly counterbalanced by the weight of the adhering liquid elevated between them, while the horizontal component is free to draw them together.

So, likewise, the column of liquid sustained in a capillary tube can have no tendency to lift the tube;' for it is evident that the weight of the liquid elevated must exactly balance the vertical component of the capillary forces acting at the crowning meniscus within the tube: the horizontal component tends to draw the sides of the tube together.

It is freely admitted that my explanation of this class of phenomena may be imperfect, and may be more or less unsatisfactory; but it seems to me that its shortcomings are not to be found in the directions indicated by the objections put on record by the critic. Such elementary facts as have been elicited above could not appropriately find a place in my paper.

After all, however, the simplest method of reducing this class of phenomena to the reaction of elastic films of liquids is the application (as has been done near the close of my paper) of the principle of Gauss; viz., that this reaction "always tends to reduce the surface to the smallest area which can be enclosed by its actual boundary." JOHN LECONTE.

Berkeley, Cal., March 16, 1883.

A new lecture experiment.

It has long been known, that an iron bar may be permanently magnetized by holding it in the direction of the dipping-needle, and striking it a blow with a hammer. The novelty of this experiment, so far as I am aware, consists in indicating the magnetization of the bar at the instant the blow is delivered. I use for the purpose a reflecting galvanometer (Kohlrausch's pattern), a lantern with detached lens for focusing the reflected beam (or, in the day-time, a porte lumière), a piece of gas-pipe 80 cm. long and 45 mm. diameter, and a coil of fine wire large enough to slip freely over the gas-pipe. After carefully demagnetizing the gas-pipe, the coil of wire is connected with the galvanometer, and slipped down against the hand, holding the pipe about 30 cm. from the upper end. With the pipe pointing in the direction of the dipping-needle, a ringing blow is struck on its upper end, and the spot of light on the screen moves promptly from two to four feet, according to the distance of the screen from the galvanometer. A second blow produces only a very small movement compared with the first one. Reversing the gas-pipe, and again striking it, the change of magnetism is

indicated by another induced current about equal to the first. The direction of the current is the same as is obtained by moving the coil from the end struck toward the middle of the pipe. By moving the coil along the pipe, before the blow and after it, the induced currents indicate that the temporary magnetism of the pipe produced by terrestrial induction is much weaker than the permanent magnetism produced by the blow. H. S. CARHART. North-western university, March 20, 1883.

HOUGHTON FARM EXPERIMENTS. Houghton Farm. Experiments with Indian corn, 1880-81, with a summary of the experiments with wheat for forty years, at Rothamsted. Cambridge, Riverside pr., 1882. 75 p. 1. 8°.

Agricultural physics. Series i. Nos. 1, 2. Meteorology and soil-temperatures. By D. P. PENHALLOW, B.S. Newburgh, Ritchie & Hull, pr. [1883.] 57 p., 5 pl. 1. 8°.

BESIDES the intrinsic value which these publications have as reports of carefully conducted experiments, they possess additional interest to all who have at heart the advancement of scientific agriculture in this country, because they are the first public reports of what is here a novel undertaking. The proprietor of Houghton Farm, Mr. Lawson Valentine of New York, has, in effect, established upon it an experiment-station devoted to the scientific investigation of agricultural questions. So far as we are aware, this is the first institution of the kind in the country supported by private munificence, and hence untrammelled by the demand for results of immediate practical utility, and by the mass of miscellaneous chemical work which seriously circumscribes the scientific activity of public experimentstations. The outcome of this form of the 'endowment of research' will therefore be awaited with much interest.

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The first of these reports gives an account of the field-experiments with Indian corn, executed by Dr. Manly Miles in 1880 and 1881. These experiments are, in the main, modelled after the famous Rothamsted experiments of Lawes and Gilbert, and are to be continued through a series of years, with the design of doing for Indian corn what the English experiments have done for wheat and barley. experimental plots having been laid out and drained in the previous year, a crop of corn was grown in 1880 without manure, in order to test the uniformity of the soil and establish a basis for subsequent comparisons. This was followed in 1881 by a crop to which various kinds and quantities of manures were applied on the several plots, certain plots being left unmanured for comparison.

Unfortunately the season of 1881 was extremely dry, and the manures applied produced scarcely any appreciable effect; so that, although various minor results of interest and value were obtained, the main object of the experiments was scarcely at all advanced by the year's work. The most interesting of these minor results is, perhaps, the striking and beneficial effect exercised on the yield of some of the plots by the thorough drainage which they received. Barnyard manure was the only fertilizer which produced any noticeable effect; and this is ascribed rather to its physical action in making the soil more retentive of water than to any direct fertilizing action.

It is evident that circumstances have conspired to render this simply a preliminary report, whose value consists in its account of the plan and methods of the experiments more than in any results yet attained.

Dr. Miles appears to be fully aware of the complex nature of the problems attacked, and to have taken great care to execute all the operations of tillage, planting, cultivation, and harvesting in a uniform manner on the several plots. He is cautious, too, in drawing conclusions, and not in haste to attribute small difference of yield to the effects of different fertilizers, as is too often the case.

His method of comparing the yields of a manured and an unmanured plot is novel and interesting. Instead of assuming the difference between the two to represent the effect of the manures, as is usually done, he first grows a crop on all the plots without manure. In the crop of the succeeding year, he first notes the gain or loss of yield on the unmanured plot, and then assumes, that, if the plot to be compared had not been manured, its yield would have varied to the same extent. Then the difference between the actual yield of the plot and what it would have yielded without manure is regarded as the effect of the fertilizers applied to it. The following example illustrates the method:

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yields; but it also involves errors of its own, and not only that, but errors of unknown amount. Because plot 3 yielded one bushel per acre more than plot 1 in 1880, it is by no means certain, that, in the very different season of 1881, the same difference would have been observed indeed, it is highly probable that it would not have been. Dr. Miles recognizes this, and designates the 7.3 bushels of our table as 'probable increase produced by manures.' But he gives us no means of knowing whether this amount is within or without the limits of error; that is, whether the manure on plot 1 actually did produce an effect or not. This cannot but be regarded as a serious deficiency in these otherwise valuable experiments; and it is one that no care in the execution of the experiments can do any thing to re

move.

A field-experiment with fertilizers involves one of two assumptions, either that the several plots have exactly the same crop-producing power, or that the differences observed in a preliminary unmanured crop are constant. Neither of these assumptions is true. With the greatest care in the selection of plots, very considerable differences in both respects will show themselves. Such being the case, the scientific conduct of a field-experiment requires that the amount of error involved in the above assumptions shall be determined, to the end that we may know whether the apparent differences in the effects of the fertilizers have any real significance. This may be done by multiplying the number of plots which receive the same treatment, and distributing them uniformly over the experimental field; the only limit. to the multiplication being that imposed by practical considerations of the possibility of treating a large number of plots.

In this way it is possible to obtain, not only the average yield of a certain fraction of an acre under particular treatment, but the amount of variation from that average which may be expected in individual cases. This method calls for a multiplication of the manured, as well as of the unmanured plots: it greatly increases the labor of conducting a field-experiment; but the results, once obtained, are reasonably accurate, and we know how accurate they are.

This whole subject has recently been very thoroughly discussed by Wagner; and a perusal of his papers1 cannot fail to be in the highest degree interesting and suggestive to all who contemplate making field-experiments.

1 Journal für landwirthschaft, xxviii. 9; Landw. versuchsstationen, xxviii. 123.

The account of the Rothamsted experiments on wheat, from the pen of Mr. Lawes, which is appended to the report, will be read with special interest, as showing what important gains to our knowledge may result from such experiments as those initiated at Houghton Farm.

The papers on agricultural physics contained in the second report relate to local meteorology and soil-temperatures. Under the first of these subdivisions the most interesting statement is, that local predictions, based on the signal-service and on local observations, were made at noon for the succeeding twenty-four hours, with only two per cent of error. Confidence in them was established, and they served an important purpose for the time during which they were issued. The observations on soil-temperatures will, of course, yield more trustworthy averages when based on more than a single season's work; but results of value are already obtained. Eight thermometers with the bulbs immersed in oil within wooden cases, to prevent change of record during their observation, were placed at the surface, and at depths of three, six, and nine inches, and one, three, five, and eight feet, and were observed hourly between seven A.M. and nine P.M., from May to October, 1882, and sometimes throughout the twenty-four hours. The soil was gravel upon hardpan and clay. The observations are elaborately discussed by Mr. Penhallow, who obtains the following results. The penetration of the surface-heat to a depth of three inches requires one and a half to two hours; to one foot, eight to ten hours hence, at a little greater depth than the latter, the diurnal waves of temperature would be reversed. Hourly change of temperature ceases at about eighteen inches, and daily, near eight feet; but these, as well as the average daily variations, being only for the hours from seven A.M. to seven P.M., need supplementary observations to show their full measure. use of minimum thermometers would greatly increase the value of the results. Irregularities in the daily temperature-curve are considered first as shown in a diminished total variation (mean depression of hourly variations'), and, second, as seen in marked irregularities in the curve (sudden depressions'). The first of these is found to be always connected with rainfall and consequent excess of moisture in the soil, probably aided by absence of direct sunshine; the second generally comes either from a temporary obscuration of the sun, as by a passing cloud, or about as frequently from the reaction after a sudden rise

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of surface-temperature much above that of the soil below.

Of more interest are the comparative results of observations made in June, three inches below the surface, in one uncultivated, and two plots of cultivated ground, referred to in the report as a and b. One of the cultivated plots, a, had been treated with composted stable-manure; the other, b, with an equivalent mixture of commercial fertilizer; and both were planted with corn. The uncultivated ground had the greatest daily range, chiefly from its higher maximum temperature; plot a had the least range, as its minimum was to 1° C. higher than in plot b. This diminished variation would seem to result from heat evolved by the decomposing manure.

All the observations are neatly recorded in tables and diagrams. Their only inconvenience arises from the use of even numbers of feet or inches in determining the depths for observation, while the records are kept in fractional centimetres; so that 3, 6, and 9 inches are always rendered 7.6, 15.2 and 22.8 cm. One system or the other should be fully adopted. As the first season of observation includes only the warmer months, studies of frost are not yet published.

FOSSIL ALGAE.

Apropos des algues fossiles.
Apropos des algues fossiles. Par le marquis de SA-
PORTA. Paris, Masson, 1882. 76 p., 10 pl. 1.4°.

In a fine imperial quarto, the author critically examines the nature of some impressions described by phytopaleontologists as remains of fossil Algae, but which a Swedish naturalist, Nathorst, in a considerable work published at Stockholm (1881), has considered as representing tracks of invertebrate animals. In his memoir, Nathorst illustrates by a large number of figures the tracks and impressions which the author himself and others have observed, as produced by the movements of small crabs, insects, worms, even of water-currents and waves, upon sand, or soft, muddy surfaces. As points of comparison, the Swedish author gives a list of the works where, to his belief, are represented so-called Algae corresponding to his figures. Among the memoirs quoted in the list are Saporta's Paléontologie française (vol. i.) — where, among the Jurassic plants, all the Algae, excepting Itieria and perhaps one or two others, are considered as true tracks and the Evolution du règne végétal, by Saporta and Marion, where most of the impressions described as Algae are regarded as tracks of divers kinds. It is to defend his

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position, and that, indeed, of phytopaleontology, that Saporta has prepared a really noble volume. He first examines the conditions of the vegetable remains, their mode of preservation, the evidence of their vegetable nature compared with the impressions produced by animals or mechanical agency. On this subject he adds a note of Dr. Marion, who has followed the same line of research as Nathorst, in carefully studying the character of the cells produced by animal agency, and who points out the great difference between these tracks and vegetable impressions. The second part of Saporta's memoir contains a detailed examination of some types of fossil Algae. The species described are represented, as well as their living related types, with admirable care and precision. Some of the documents from which Saporta has derived valuable assistance are from the works or communications of American authors; Harlania Hallii, among others, is beautifully figured. With few exceptions, all the evidence adduced in the admirable work of Saporta is opposed to the opinions of Nathorst, and renders great service to phytopaleontology.

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first, whether the analyses given are typical ones, such as would enable the student, on the completion of the course, to work out by himself the common problems of quantitative analytical chemistry; second, whether the notes given under the various determinations are such as explain, not only the different steps of the process, but also the reasons that necessitate them. The first of these two questions we can answer decidedly in the affirmative. The only criticism that we might make is, that possibly too much attention has been paid to alloys, and not quite enough to complex mineral determinations. The first analysis given is baric chloride, then magnesic sulphate, and other simple salts where no process of separation is necessary. The book then takes up, in well-chosen order, almost all the common alloys and minerals, gives the simpler problems of volumetric work, the determination of carbon, hydrogen, and nitrogen in organic compounds, and many of the most striking commercial tests; such as the examination of sugar, milk, mineral-water, coal, and petroleum. The notes, however, under these different analyses, we cannot consider as perfectly satisfactory. They consist of a short account of the process, with references to Fresenius or the original article, and sometimes a tabulated plan; but no explanation of the various steps is given. If, after each analysis, the reasons why the different reagents had been added, and other numerous details, had been explained, the value of the book would have been much greater; for it is the want of such elucidations in Fresenius that makes his system seem confused and difficult to the young student. whole, however, when studied, as intended by the author, in connection with Johnson's translation of Fresenius, or when supplemented by a thorough series of lectures, we can recommend the book as giving a valuable course in quantitative work.

As a

WEEKLY SUMMARY OF THE PROGRESS OF SCIENCE.

ASTRONOMY.

Encke's comet, and a resisting medium in space. — Dr. O. Backlund, in a paper entitled Kurzer bericht ueber meine untersuchungen ueber die hypothese eines wiederstehenden mittels (Mélanges math. et astron., vi.), makes the following statement of the results of his researches on Encke's comet: "The investigations hitherto made of the theory of Encke's comet really prove nothing as to the existence of a resisting medium in space. Even if we

should succeed by such a hypothesis to explain sufficiently the increase of the mean motion and the decrease of the eccentricity during the period 181948, a simple hypothesis like this will not at the same time suffice for the motion of the comet after 1865, as the variation of the mean motion after that time has most probably become different. Not until the period 1865-81, and its connection with the earlier one, have been fully discussed, will it perhaps become possible to find indications of the nature of the unknown forces which act on the comet." (Copernicus, Feb.) D. P. T. [531

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