In the curriculum of studies recommended by him, Mr. Fitch has strangely subordinated, if he has not greatly ignored, the studies that prepare the citizen for his duties as a member of the State-the Social and Political Sciences. Surely he has not read, or greatly studied, the admirable pleading in their favour to be found in the works of his friend William Ellis, and also of George Combe, as recently fully presented in his educational contributions, edited by one of his colleagues in the inspectorate. In this respect, there appears to us to exist a serious hiatus in his plan of study. One of the doctrines he enunciates is also enough to raise the old phrenologist from his grave, what he calls "the convertibility of intellectual forces," whereby, he informs us, "every kind of mental power, once worked and applied to a worthy purpose, becomes available for other purposes, and is capable of being transformed into power of another kind”—an ancient error in schools, still fruitful of failure and wrong, which we are surprised to find held by a man so generally wise on education. Poor George Combe otherwise fares sadly at the hands of Mr. Fitch, who describes his mission in life as being that of advocating the one doctrine of inherent hereditary aptitudes, and says that "he never could induce his friends seriously to attempt the classification and teaching of a school on his principles, and the experiment yet remains untried"! What of the history of such schools given in the work on Combe's principles just named?

Though not agreeing on many points with the author, as was inevitable in a field so full of controversial matter as the growing science of education, we look upon the book as a valuable contribution to the subject, which, by its unusually attractive style and high tone, will command a wide audience, and, from the auspices under which it is produced, will reach places where sound educational philosophy too seldom penetrates. We cordially recommend it to all interested in education, and specially to teachers; and also to the active Education Society, as, like Prof. Bain's recent work on Education, which they have already taken up, an admirable basis of profitable discussion.

PRACTICAL HISTOLOGY

A Text-Book of Practical Histology, with Outline Plates. By W. Stirling, M.D., Sc.D., F.R.S. E., Regius Professor of the Institutes of Medicine in the University of Aberdeen. (London: Smith, Elder and Co., 1881.)

A

T the outset Dr. Stirling informs us that "the purpose of this work is twofold: first, to give plain, definite, and precise directions for the preparation and examination of the animal tissues; and secondly, to ensure that the student executes a drawing of the majority of the microscopic specimens which he makes for preservation. For this purpose a series of Outline Plates is issued with the text."

As regards the first of these objects, there is no doubt that to give "plain, definite, and precise directions" is a

"practical" books strive to attain. Those that succeed in this endeavour differ from one another chiefly in the means by which this object is accomplished; in some the author arrives at his object after long-continued patient and diligent work, in other rarer instances he utilises the works of others, and by doing so he may, and sometimes actually does, produce a book which has considerable merits of its own, inasmuch as it gives in plain and simple words valuable and useful extracts of much larger original works full of minute and bewildering details, not easily understood by, and of little practical use to the ordinary student. Dr. Stirling, although his book cannot in any sense claim to be considered other than a book of compilation, has nevertheless succeeded in presenting to the medical student, anxious to acquire the necessary amount of knowledge in practical histology, a work which, conveying in a short and intelligible manner a great deal of information, will, we doubt not, prove of service.

As regards the second object of the book, viz. that the student should for himself make drawings of his microscopic specimens, we fail to see how Dr. Stirling's Outline Plates can advance this object in a satisfactory manner. We always thought that the student drawing the correct outlines of the specimens or of parts of the specimens prepared by himself, has got everything that is essential to guide him in the study of those specimens. To fill in the details in pencil, or, as Dr. Stirling suggests, and what is still more laborious, in colours, in the outline figures drawn for him from somebody else's specimens, appears to us of more than questionable value.

Besides the directions for practical work a considerable part of the book is taken up by the description of the structure of the simple tissues and organs. As far as we can see, these descriptions are in a great measure, to the extent of verbal quotations, borrowed from other books, without even an attempt to mention this fact; by doing so Dr. Stirling has deviated from the accustomed rule and has proceeded in a rare and unexpected manner. If an author introduces abstracts and verbal quotations from any other work, we believe it will be universally admitted that whatever the aim and nature of the book, the author is bound to mention his source; if he omits to do this, intentionally or unintentionally, he lays himself open to the charge of having committed what in the eyes of every right-thinking man, not to say of every man of science and teacher in a responsible position, must ever be considered a grave offence.

Dr. Stirling has made very extensive use of the "Atlas of Histology" in some chapters, e.g. on the salivary glands, the kidneys, the generative organs, and others, making copious extracts therefrom, to the extent of verbal quotations, without in any way indicating that he has done so.

Dr. Stirling's proceeding is greatly to be regretted, since by his numerous and original works in histology he has won the esteem of his confrères and has proved himself to be sincerely anxious about the promotion of

LETTERS TO THE EDITOR [The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts. No notice is taken of anonymous communications. [The Editor urgently requests correspondents to keep their letters as short as possible. The pressure on his space is so great that it is impossible otherwise to ensure the appearance even of communications containing interesting and novel facts.] The Electric Railway in Paris

I HAVE within the last few days received a letter from a friend in Paris, who writes that he had last week travelled on the electric railway in that city. There is still much, he adds, to be done before it can be brought into general use; but nevertheless the train moved satisfactorily. There were fifty-four passengers in the carriage, which was propelled by a large Gramme machine and 160 cells of Faure's battery. The experiments are to be recommenced very shortly with a new motor by M. de Méritens, and a Faure's battery. W. SPOTTISWOODE

41, Grosvenor Place, S. W., June 16

Probably New Variable and Red Star

ON May 22 I found, 2° 51'7 north of a Cygni, a deep red or crimson star, which is not in the Bonn Catalogue. The nearest to it there is + 47° 3167, which in declination corresponds with a white star that I observed at the same time, but not in R. A. Dr. Doberck writes to me as follows: "Markree Observatory, 1881, May 29; observed the new star; brick-red, the nicest I ever saw, 87 mag. ; and "1881, May 31: 1h. a.m., colour same as before; 8'4 m.'

Mr. Ward of Belfast, who observed in the early morning of May 31 in strong twilight, describes the star as "deep crimson; beautiful object; two or three comites."

Mr. Gledhill, in Mr. Crossley's observatory, Halifax, found it, on May 30, "strikingly red.'

Dr. Ball, the Astronomer-Royal for Ireland, observing at Dunsink, saw it "a superb crimson."

Prof. Krueger, director of the Kiel Observatory, described it as" auffallend roth" (remarkably red), on May 30.

On June 2 it appeared to me unchanged in colour, and increased from 9 mag. to 8'4.-June 7 and 8, colour still the same, and 8.3 or 8'4 magnitude.

Dr. H. Kreutz, writing from the Bonn Observatory, states that he finds an observation of the star recorded on June 19, 1857, but not at any other time during the progress of the observations for the Bonn Catalogue, in which it has not been published. There does not appear to be any note of its colour, and I think it will most likely prove a variable of a very remark. able character. Prof. Krueger makes its position for 1855 = a 20h. 36m. 37s. ́9; § 47° 37′ 33′′. Herr Kreutz's position is a 20h. 36m. 37.0; 8 47° 37'9. The white star mentioned above is not recorded in any of the Bonn observations; and, on the other hand, I may add that I do not identify + 47° 3167 in the telescope. I estimated the white star at about 9'5 mag. of Argeländer's scale, and therefore within the limits of the Durchmusterung.

The small stars seen by Mr. Ward are perhaps too distant to be strictly considered as comites to the red star. They are sufficiently difficult to me, though probably easy to his wellknown extraordinary sight. The position of the nearest that I see is about o°, and I find two others more distant-one at 350°, and one at 110°, with a power of 120° on a 4 inch O.G.

There seems a peculiar dimness about the star, referable, probably, to the dark shade of its red. An uneducated person with a very excellent eye, and who never heard a description of a red star, compared it, at first view, to "a drop of black blood." It may be conveniently and well compared with Nos. 448 and 553 of my "Red Star Catalogue," especially with the former, the colour of which was described by Secchi as "intense"; and in the glowing red of the one object will be remarked a striking contrast with the deep sombre tint of the other.

I make the approximate positions of the red and the white stars for 1855, and corrected from my first observations, as follows:

The Doctrine of the Conservation of Electricity I WISH to take the earliest opportunity of responding to the courteous letter of M. Lippmann, which appears in the current issue of NATURE, with the acknowledgment that his quotation from the Comptes rendus of 1876 establishes in the most conclusive manner his priority of date in the enunciation of the doctrine of the Conservation of Electricity. As to my own independent enunciation of this doctrine, it was arrived at without any knowledge of the comparison drawn by M. Lippmann in 1876 between the cyclical flow of heat (of Carnot's theorem) and the cyclical flow of electricity. I approached the matter upon somewhat different and less clearly defined lines, and finally struck upon the fundamental notion of the Conservation of Electricity when endeavouring to think out the relations between electromotive and ponderomotive force in an electric theory of radiation based upon Clerk-Maxwell's Electromagnetic Theory of Light. My speculations on this point were committed to writing some weeks ago, and will shortly be published. I content myself in the meantime with pointing out how near Clerk-Maxwell came to a similar conclusion. In Article 35 of his well-known treatise, he says emphatically: "While admitting electricity, as we have now done, to the rank of a physical quantity, we must not too hastily assume that it is, or is not, a substance, or that it is, or is not, a form of energy, or that it belongs to any known category of physical quantities. All that we have hitherto proved is that it cannot be created or anni hilated" (the italics are mine). Nevertheless the immediate and logical conclusion that electricity, like matter and like energy, is subject to a law of conservation, appears to have been rejected by Clerk-Maxwell for reasons explained in Article 574 of his treatise, consequent on his inability to discover whether an electric current possessed momentum or could exert a mechanical reaction upon the matter of the conductor through which it flows. The unfortunate dilemma which suggested this experiment could hardly have been raised if it had then been as clearly understood as it now is that there is the same distinction between electrokinetic and ponderokinetic energy as between electromotive and ponderomotive force. But to discuss this matter further would lead me to take up too much space. SILVANUS P. THOMPSON

University College, Bristol, June 19

Thought-Reading

Two

IT would seem that the "discovery" of reading people's thoughts, lately mentioned in the daily papers, is in no way essen tially different from the well-known "game" of "wishing" often played by young ladies. It consists of the following procedure. One person goes out of the room, while others arrange upon what she is to do. She enters blindfolded, and in the particular instance now alluded to, was turned round several times so as to be quite unconscious of the direction in which she was facing. persons now place their hands on either side of each shoulder, making their fingers meet at the back of the neck and under the chin; or they may be placed round the waist; but as the forehead appears to be equally sensitive, perhaps it is immaterial where the hands be situated. After standing still a moment or two, the lady moved slowly round in the direction of a sofa under the impression, as she afterwards said, that she was walking in quite another way. Having reached it, she sat down (not even knowing the sofa was close by), and deliberately put out her hand, took up an antimacassar which lay upon the sofa, and raised it, asking, "Is this what I was to do?" This was perfectly correct, the antimacassar having been expressly laid there for the purpose.

It was settled that another lady should walk into the conservatory. To do this she had to pull up a blind, lift an iron bar and open the shutters, then undo the glass door behind them which led into the conservatory. All this she did unhesitatingly, and walked straight into it. I could describe several other instances where ornaments and other things had to be selected out of various groups of objects, &c.: but the above will illustrate the process.

One essential condition of success is that the individual must voluntarily and entirely surrender the will, while those who hold the person blindfolded must determine as powerfully as they can that the latter shall do what they wish. Care should be taken not to push the individual in the desired direction. This however may be done involuntarily, but it will not account for the person doing all that has been previously determined after

arriving at the spot. Some ladies describe a remarkable sensation accompanying the proces: a sort of "all-overishness," or even faintness, so much so that the lady first alluded to on one occasion staggered, and could not proceed at all.

It appears to me to be a very peculiar psychological phenomenon well worthy of investigation, if possible, but too well known to be disputed. GEORGE HENSLOW

66

6, Titchfield Terrace, Regent's Park, N. W. P.S.-Since writing the above I have heard of a much more remarkable case than the preceding. The operators sat in a circle, silent, but determinately willing" that a certain lady should do what they had resolved upon. She stood in the centre, and was not blindfolded or touched by any one. In every case she did it correctly. One thing that was agreed upon was for her to take a bottle of wine from one table, carry it to another, and pour out a definite quantity of wine. This she did, not exceeding the amount predetermined. On a second occasion she had to find a key hidden away behind some books. As she approached the place she became very excited and hysterical, but at once extracted the key.

The above cases clearly show that as far as they are concerned "thought reading" is an incorrect expression, as the person operated upon is a passive automaton, while others, as it were, force their wills upon her. "Will-imparting" would seem to be a better term.-G. H.

--

Notes of the Cuckoo

IN a letter appearing in NATURE, vol. xxii. p. 76, I stated that "All the cuckoos here intone in a minor key except one, which alore does not flatten the 3rd of the tonic. The key is in all cases precisely D of concert pitch, as proved by a tuningfork, and the first note is F on the fifth line." This year I find that, while the cuckoos here generally intone in D minor, as above, there is one again that intones in D major, and two others in C major and C minor respectively. Some that I casually heard in other places in the neighbourhood intoned in D minor. Millbrook, Tuam, June 1

JOHN BIRMINGHAM

Notes on the Indian Glow-Fly HAVING failed to find any critical description of these interesting insects, it is possible that the notes I am now able to send you may cause others to enter the field of inquiry. Situated some 2900 feet above the sea, and in Central Southern India amidst hills, valleys, and streams, I have had peculiar opportu nities for observing them.

They are not to be seen during the daytime, but so soon as darkness steals upon twilight, so surely do these small natural lanterns become visible, and their numbers rapidly increase, much indeed as the visibility of the stars increases as the evening passes into midnight.

The fire-fly, when examined individually, is by no means a pretty-looking insect, and comparing it to other insects and flies, it is certainly both large and ungainly. An ordinary house fly is five-sixteenths of an inch in total length and weighs 25 grains, but the subject of my notice has a total length of nine-sixteenths of an inch and weighs 66 of a grain; we thus at once learn something as to his size and weight. The glow-fly-or beetle as I should term it—has a black head and antennæ ; the thorax and abdomen are of a yellow-red colour. This latter part of the insect's body is divided into six rings, and, counting from the thorax, it is the fourth ring that emits the light. There is a rectangular opening in this ring which is merely covered by a very thin skin; it is in fact a window from which the light emerges. The insect has only one pair of wings: these are small, most delicate and thin, and are sheathed. It is worthy of careful notice that these insects fly both rapidly and slowly, but make no noise or buzz in the air. To test this further I have frequently liberated several of these glow-beetles in my bedroom, and in the dark they have only appeared as fairy stars, as no humming could be detected.

As regards the character and quantity of the light, I have to observe that one insect enables me to see the time by a whitefaced watch when four inches distant; twelve of them placed in a glass jar enable me to read a book with ease, and are equal to a small Geissler's tube. The light is of an exceedingly beautiful colour-a sombre yellow tinged with green, but at intervals it is brilliant. A preliminary examination of the light in the spectroscope (a large one made for me by Browning) shows a distinct

clear continuous spectrum, no lines or bands of any kind being visible.

The insect made to crawl on a card placed over the poles of a powerful compound permanent magnet showed no signs of uneasiness or change of light. Similarly placed over an electromagnet (ten Grove cells) and rapidly alternating the current caused no change. Placed within a coil of covered wire, no change. Blowing very gently, my breath on the insect caused no change; this was also tried with a blowpipe. Cold air at 50° caused a distinct diminution of the light; on the other hand, air at 100° caused an increase of light.

I now placed several of the insects in a bell-jar, and gave them a good supply of clean oxygen gas; the luminosity at once increased fully 25 per cent. On a dead insect (which still sheds light) oxygen gave similar results, and on extracting the luminous part and blowing oxygen upon it the light was much increased. It will prove interesting to mention that, so soon as darkness has fairly set in, millions of these insects invade the trees, and as my bungalow is near to a stream and level with the tops

The

of the trees, I am able to notice them with much care. curious pulsation or flashing of their light is remarkable: the insects resting on the tree all act in perfect concert, i.e. five seconds of no light, then seven rapid flashes; five seconds, no light, seven flashes; and so the game continues throughout the dark hours.

At first I had reason to believe that the insect when flying only emitted light; this however is not the case; for when observing the Pole Star for variation with my theodolite, it occurred to me during a passing cloud to turn a telescope on to the glowing tree. At once I had the field of view filled with tiny stars, but both fixed and wandering.

It is also worthy of special notice that all the glow-insects on a dozen or more trees will continue to keep up the most perfect time as to the flashing of their light and the interval of pause, and this for many consecutive hours; but this singular agreement as to the time relates to close clusters of trees only. Thus distinct groups of trees separated by one or more hundred yards may not agree, and do not do so as a rule.

I have been informed on safe authority that the Indian bottlebird protects his nest at night by sticking several of these glowbeetles around the entrance by means of clay; and only a few days back an intimate friend of my own was watching three rats on a roof rafter of his bungalow when a glow-fly lodged very close to them; the rats immediately scampered off.

In conclu ion, these insects see by day as well as by night, and I incline to the idea that the beautiful light they carry serves as a means of intimidation or protection, and certainly as a means whereby to recognise friends.

As I gaze from my verandah down the Nadgani Valley into the dark night I see the pulsations of light here, there, and everywhere! and as my optical powers increase so do these gaseous, nebulous patches become resolved into real living

stars!

Wynaad, India, May 5

H. A. SEVERN

Birds Suffering from Cold THE unusually severe weather (5° 12° Réaumur) of these last twelve days struck heavily on the swallows of our country. They have been found dead by hundreds. The distress of the poor animals must have been extreme. Suffering from hunger and cold, they pressed against the windows, and being brought in suffered to be petted and fed, but died from exhaustion. In Kopidlno about 300 took shelter under a balcony, and the cold growing more and more intense towards night, they clustered on each other like bees until morning, when thirty were found dead. I have been walking this afternoon in the suburbs of Prague, where a fortnight ago I have seen swallows skipping on the river and hunting in gardens, but although the weather was now clear and warm, I could not see a single one. Tidings of suffering swallows come from the country, where people have been kind to them, feeding them on ants' eggs and flies, but they would not eat, and died. In some nests the young ones were found starved alone, in others their mothers were with them. J. V. SLÁDEK

Prague, June 16

An Optical Illusion

THE illusion of the inverted pin was shown me about the year 1846-47, and I well remember, when I was at Cambridge,

working out the explanation inductively. In the autumn of 1847 I was spending an evening with Dr. P. M. Roget, at his house in Woburn Square, when among other subjects we conversed upon was that of optical illusions. The inverted pin was one of his illustrations, and I think he mentioned having explained it in some scientific serial.

Some years ago the late Mr. Becker, formerly scientific foreman to Messrs. Elliot Brothers, constructed for me a binocular apparatus for showing the union of two shadows, one on each retina. To my surprise I found the resulting phantom did not differ in position from the single shadow. C. M. INGLEBY

Athenæum Club

How to Prevent Drowning

I ONLY write in the interests of humanity. Let those who will go in for swimming, and I wish sincerely that every one could swim. Treading water however conducts at once to swimming. Every one can tread water who likes. It is just as easy, if we only knew it, to tread water as to tread the earth, and proximately just as safe. Men and women might walk into the deep sea and out again when they pleased. Nature has not been so niggard with us as some persons imagine. Why are we not as safe in water as is the dog? It is simply because he treads water, and we do not. As often as I chose to chuck my stick into the Causey surge my dog brought it out. I could have done the same; any one could do the same who chose. But assuredly I should have paddled water as the dog did. In treading water the body is erect, or nearly so; in swimming we sprawl, and are comparatively helpless. The admirals, both of them, have given valuable testimony as regards the efficacy of treading water. Before the present pier at the Cape was built, vessels in bad weather could not communicate with the shore, even by boats. Men, then, treading water amid the mountain seas, carried communications to and fro in oilskin caps. have heard it was the same at Madras. Young Gordon, apprentice to the sea, fell into mid ocean while fisting a sail. The poor fellow's heart sank when he saw the ship sailing away. But, as he afterwards told me, he trod water, and kept up till the boat reached him. I have trodden water again and again with a big boy on my back. Any one might do the same. Not one woman in ten thousand, not one man in a thousand, I suppose, can swim. They do not know they can tread water when they fall in, and of course drown, as two fine young women who had got a little out of their depth in this place did last year. But ignorance and prejudice cannot always rule, and the day will surely come when human beings, better instructed, shall enjoy the same immunity in the water that other animals not human beings, now enjoy. HENRY MACCORMAC

Bournemouth, June

Buoyancy of Bodies in Water

I

A propos of the question of drowning, as the same is now raised in NATURE, and especially so as to the alleged "fact that men are very different in buoyancy," allow me to say that when stationed many years ago at Pembroke Dock, South Wales, two soldiers were drowned there within a few days of each other. One of these casualties occurred off an island named the Stack Rock, in Milford Haven, that was garrisoned by invalided artillery, while the other took place in the creek that separates the town and dockyard from the huts. In the former instance the body of the (drowned) man remained floating upright in the water, "bobbing up and down with every wave -as an eyewitness assured me--for a considerable time, or until it was lost to sight or recovered (I forget which just now). In the latter the body-that of a healthy, muscular man-was picked up a day or so afterwards by a passing boat as it was floating out with the tide to sea; and I have since seen several fresh bodies floating in the Ganges. Indeed the survivors always attach weights to the remains of even the poorest of their kindred ere they deposit them in that sacred stream; but this may be for the purpose of counteracting the current; and it is, I think, generally assumed in books and courts of law that all bodies, human and bestial, sink as a rule in water as soon as life is extinct; in other words, it is stated that they remain submerged till decomposition sets in, or sets up such an amount of gas within them as enables them to overcome all resistance from above, and float. If such be the case we must either suppose that the corpses referred to within possessed some special attributes of their own, or that "men are very different in buoyancy" after death than they were during

life. Assuredly these men could not have been lost in this way had their bodies been able to float in the one state as well as they were in the other; and I heartily agree with Mr. Hill when he says that "no amount of coolness or presence of mind will either supersede the art of swimming or alter the laws of gravity." Ashton-under-Lyne W. CURRAN

Resonance of the Mouth-Cavity

THE observation of Mr. John Naylor, forwarded to you by Mr. Sedley Taylor (p. 100), admits of being made with more striking (because louder) results than by the method described, and so far from being a "discovery," is well known to most schoolboys. Tap with the thumb-nail upon the front teeth, and at each tap alter the shape of the mouth-cavity so as to produce the note desired; any tune may then be played loud enough to be heard at the other end of a large room. It is remarkable that without previous practice one instinctively shapes the mouthcavity so as to produce, in almost every case, the exact note required. GEORGE J. ROMANES

"The storm set in about 6 p.m., whilst the men were at stables, and was accompanied by loud thunder and vivid flashes of lightning. At 6. 15 there was a fearful roll of thunder, accompanied by a most vivid flash, which lit up the square for at least thirty seconds. It struck the barracks at the upper end, ran past a room to the stables, which have iron roofs; it ran along the course of the roofs into the stables, striking down two men in the doorway. It then ran along the iron of the manger, flooring all the horses, nineteen in all, and so went to ground. One man was struck in the left shoulder bone, the fluid passing from there under the left arm to his watch in the left-hand trousers pocket, and burnt a hole clean through the silver case. From the watch it struck again six inches below, and travelled round the leg under the knee, and from thence probably to the spurs, as no burn was found below the knee. The extremities of both tracks were marked by large burns, and each track by a burn two inches over. The surgeon says it was the most miraculous escape he ever saw, the watch having saved the man's life. The second man was merely stunned, and lost the use of his legs for some hours; he was standing in the stable behind the first, and although only slightly burnt, is still unable to walk. The other is doing well, but is rather dazed. Ten other men were floored, but soon regained their legs. As to the horses, one was struck dead in the forehead: two others, blind in both eyes, were shot yesterday; and four more blind in one eye are condemned. A horse in town was struck, and his fore-leg broken in four places.

"Within a hundred yards of the barracks is a powder magazine full of powder, fitted with conductors which were struck several times. This occasioned great alarm to the inhabitants, as it contains many tons of powder.

66

'JOHN P. CUNNINGHAM 'King William's Town, South Africa, April 18"

A Six-Fingered Family

IT may interest some of your readers to hear that there is at present living in Brown's Town, Jamaica, a family in whom the possession of six fingers has been hereditary for at least four generations. Unfortunately they consider the sixth finger a deformity, and always amputate it, so that there is very little opportunity of observing it. There is a little girl there however upon whom this operation has not been performed, and I much regret that, as her parents had taken her up into the hills to work in their provision grounds, I could not see her. As I am informed, the sixth finger springs from the little finger knuckle at right angles to the little finger, and when it is free of it, it turns up parallel to the rest, being a little shorter than the little finger, but quite perfect, with nail and two joints. It is bent and extended with the rest on opening or closing the fist.

Another fact, which I daresay however is usual in such cases,

Kingston, Jamaica, May 26

THOMAS CAPPER

be of the general form dp

Singular Behaviour of a Squirrel

A NEIGHBOUR of mine, whose cottage is thickly surrounded with trees, observed a squirrel, during the severe weather of winter, occasionally stealing food from the troughs set out for the poultry. At first it caused great commotion among the birds, but latterly they were less uneasy in its presence. Taking an interest in the wild creature he began to lay out refuse food for it, including bits of ham, which it greedily appropriated. Getting more courageous, it ventured within doors. After a time it got caught in a trap set for rats underneath the bed. Being freed from its irksome position it was thought that the squirrel would venture no more within doors. Neither the incident of the trap nor confinement for some time within a cage availed to restore to it its original shyness. With the coming of summer its visits have been less regular, but occasionally it looks in still. May not a habit like this, affecting only one out of many, be looked upon as corresponding to a sport " in the vegetable world, and shed some light on the subject of the domestication of animals? The squirrel seems to have been quite a wild one to start with, for there is no one in the district who had been in the habit of keeping one as a pet. J. SHAW Dumfriesshire

Ar dt [s - S1][273 + 1]

s and s1 = = the specific volumes of water in two different forms of aggregation].

The point m, where m n, m d, and m l unite, is of particular interest. J. Thomson called it "the triple point," and Guldberg

not

the " Fallespunkt" of water. Lately (in Berichte, 1880) I ventured to call it the "absolute point of sublimation," because I wished to introduce a new term for a well-known scientific object, but only to point out some important consequences of the phenomenon just then announced by Carnelley, of which Prof. Lothar Meyer of Tübingen had published an interpretation different from mine. This point m, situated -0°0078 C. below the ordinary freezing-point of water, is really the upper limit of sublimation, because at any higher temperature ice first changes into water before it evaporates. At -0°0078 C., where the boiling- and melting-point of water coincide, a real sublimation of ice begins, provided that the barometric pressure does not exceed 4'6 mm. (="the critical pressure" of Carnelley).

Now according to the discovery of Dr. Carnelley, ice at pressures lower than 4'6 mm. would exist by temperatures up to +178° C. Thus the surface v = f(p, t), which we have hitherto supposed to be inclosed between the limits qp, q l, 1 m, m d would extend far beyond Im nearly up to k, but always at pressures smaller than 4'6 mm. Geometrically this new and unforeseen

Hot Ice

IN reply to a very interesting letter on this subject recently published in NATURE (vol. xxiii. p. 504) by Dr. Oliver J. Lodge, I wish to express my views of the theoretical and practical possibility of the experiment of Dr. Carnelley. I wish to start from some well-known principles accepted by everybody acquainted with the mechanical theory of heat and its applications. According to these principles the volume "v" (and also the total amount of internal energy) of water can be expressed as a function of its pressure "p" and temperature ""; v = f(p, t). The form of this function, which we need not discuss here, will change with the state of aggregation, so that we shall have three different equations expressing the volumes of water in the solid, liquid, and gaseous form.

...

...

ice water vapour

and being considered independent variables.

v = fi (p, t) v = f (p, t) v = f (p, t) Geometrically the volumes of ice, water, and vapour will belong to three different surfaces extending between certain limits. Thus the surface v = f(p, t), which represents the volumes of ordinary ice, is situated between the limits qp, Im, md; the surface representing liquid water lies between mn and md, though it may be extended a little on either side of these limits, if it applies to water heated or cooled over its regular boiling or freezing temperatures, which are situated along the lines md and min. The values of p and t, which belong to md and m n, will satisfy two equations (p, t) = 0 and (p, t) = 0. At these points the water will change its form of aggregation and pass over in the state of saturated vapour along the line mn [equation (p, t) = 0], or into ice along md [equation (p,t) = 0] in a continuous and reversible way. At any other point, which is not situated on m n or md, water may also be liable to change of aggregation, but this process will not be reversible. The line mn, where the surface v = f(p, t) breaks up and liquid water changes into vapour, is the curve of tension of saturated vapour contained in the renowned table of Regnault. The boiling-points of water under varying pressure are situated on mn, and may be found by solving the equation (p, t) = o. At the point m (p = 4'6 mm., t = 00078 C.) the line mn terminates, but is continued by I m [equation x (p, t) = 0], along which the vaporisation of ice takes place in a reversible way. According to the table of Regnault there is no sudden rupture at the point m, the pressure of saturated vapour at o° C. being identically the same, if the vapour is in contact with water or with ice. The differential coefficients dp of the functions

dt

The surface corresponding to the volumes of aqueous vapour v=f(p, t) is not sketched in the figure, which gives only the projection of the surfaces on the plane of co-ordinates and t, not the real situation of these surfaces in space. The reader will also observe that the limiting lines mn, nd, Im, mk are the intersections of vertical cylindrical surfaces (Uebergangsflächen") with the plane, t.

extension of the surface of ice is represented by the area Im k. Here the process of Carnelley, whereby ice of low pressure is heated to astoundingly high temperatures, would go on. area Imk would of course be entirely a terra incognita to the science of the present day, but there is nevertheless no theoreti cal objection why the surface of ice v = f(p, t) should not extend farther than to the limiting line Im pointed out by Regnault. Confiding in the experimental proofs already furnished by Dr. Carnelley, I concluded (Berichte, 1880): if the surface of ice really extends upwards to about +178° C. there must be a limiting line m k to the area I m k, since this area cannot extend so far as to the dotted line in the figure indicating the critical pressure 4.6 mm. At this new limit, mk, corresponding to an equation (p, t)=0, the vaporisation of the "hot ice" may go on in a reversible way, just as liquid water gives up saturated vapour at those pressures and temperatures which belong to the line mn (equation ↓ (t, p)=0). The line mk would in many respects be the continuation of md (just as ml forms the continuation of m n), but naturally the symlls entering the equation of its differential coefficient dp Ar must change their signification on the other side of the point m, so that r here would represent the latent heat of vaporisation of the hot ice, s its specific volume, &c. I did not expressly mention this in my paper in the Berichte, because I thought unnecessary. This omission on my side may probably have misled Dr. Ó. Lodge as to the real meaning of my words, since he declares my opinion that an equation (p, t)=0 having a differential