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But let Here is a perfect demonstration evident to the senses. us go one step further. The rectangles in the preceding theorem may be bisected by diagonals and set round the square of the difference in such a manner as to form the square of the hypothenuse of the right-angled triangle, the sides of which are also those of the assumed squares. The squares of the sides of a rightangled triangle, therefore, are together equal to the square of the hypothenuse, since the former may be changed into the latter.

a

m

The same conclusion may be arrived at by a still shorter and simpler course. Let any two squares be joined together as in the annexed figure, or, rather, let them be cut in paper in one piece. Then take a c equal to the side of the greater square, and join b c and c e. Cut off the two equal triangles bac and cde, and place them in the positions of bmf and fne, and the two squares will be thus transformed into the square of the hypothenuse of the right-angled triangle, of which they form the sides.

Thus we have at once a demonstration of the famous Pythagorean theorem (Euclid i. 47), and have attained with three or four steps the same height climbed by Euclid with forty-seven. The words of his demonstration, committed to memory by a child, remain there mere words and nothing more. Words serve to mark and denote ideas, but cannot create them, where the material of ideas does not already exist. But the child who with paper or card amuses himself in going over the visible demonstration suggested in this letter, in various forms and repeatedly for neither old nor young can be said to learn a truth merely by its transient recognition-will assuredly awaken to an agreeable consciousness of the reasoning faculty, and feel no difficulty in future geometrical studies.

In 1860 there was published for me, by Messrs. Williams and Norgate, a little volume entitled, "The Elements of Geometry Simplified and Explained," adapted to the system of empirical proof, and of exhibiting the truth of theorems by means of figures cut in paper. It contained in thirty-five theorems the quintessence of Euclid's first six books, together with a supplement of thirty-three not in Euclid. There was no gap in the sequence or chain of reasoning, yet the 32nd and 47th provisions of Euclid were respectively the 3rd and 17th of my series. This book proved a failure, for which several reasons might be given, but it will be sufficient here to state but one, namely, that it came forth ten years before its time. What became of it I know not. But of this I am convinced, that though I failed, success will attend those who follow in my footsteps. W. D. COOLEY

THE discussion in your last part on methods of teaching elementary geometry reminds me that at a period when I was teaching the subject to a considerable number of pupils, I frequently overcame the difficulties of very young or inapt students by commencing with the study of a solid, such as a cube, encouraging the pupils to frame definitions for the parts of the object. The ideas existing in the child's mind of a solid, a plane, a line, and a point, were thus put into words in an order the reverse of that in which they would have been had Euclid been used. The chief properties of parallelograms and triangles followed, and were easily discovered by the use of a pair of compasses, scissors, and paper, and that at an age when Euclid was a sealed book. I believe children can be most easily taught to solve problems in plane geometry when they occur in connection with early instruction in practical solid geometry. Most children try to draw, and if they were encouraged to represent simple objects by "plans" and "elevations, "the necessity of obtaining knowledge of how to describe the forms presented to them would frequently carry the pupils through a large number of the principal problems of plane geometry with a pleasure they could not experience if the "problems" were put before them, without any reason for their solution but the teacher's command. The powers of truthful representation gained by such teaching, would

be of the utmost value to thousands who would never attempt to learn "Euclid ;" whilst, so far as I am able to judge, it is more likely to prepare the boy to read formal works on geometry with pleasure than to create a distaste for the study. THOMAS JONES Woolwich, October 9

The Coming Eclipse

I HAVE been very much interested in Mr. Lockyer's lecture at the Royal Institution on the late eclipse. I am especially glad that he is at length able to acknowledge the existence of comparatively cool hydrogen, because in my Eclipse Report of 1868 (vol. xxxvii. Part 1, R.A.S. Memoirs), I stated that I believed from the evidence of the photographs that hydrogen was dispersed from the prominences in visible streams in some cases, and in others invisibly.

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sun.

But while Mr. Lockyer admits this, he seems to me very unnecessarily to avoid everywhere the use of our familiar term 'atmosphere" to include the whole gaseous envelope of the This seems to me to be the sense in which Kirchhoff used the word when he said it was extensive.* It certainly was the sense in which I used it, and, I believe, that in which all who spoke of an extensive atmosphere did so use it. In this sense there can be no doubt that the sun has an extensive atmosphere, the outer portion of which is comparatively cold and capable of reflecting light if the polarisation now not doubted be due to reflection.

There is one consideration which, however, does not seem to have occurred to Mr. Lockyer. If the cold atmosphere, as I will venture still to call it, reflect the prominence light, it will also reflect the solar light. Its reflected light then should be such as reaches us at ordinary times, and not so exclusively chromospheric. Adding to this the light which is due to cool hydrogen, we should have, I anticipate, a faint continuous spectrum with the bright line F, and also a solar spectrum with, perhaps, some of the chromospheric lines reversed. That is not what has been found, and I do not at present see any way of reconciling the facts with the theory that the undoubted polarisa

tion is due to reflection.

Before going to another subject, I would wish to direct attention to my friend Captain (now Major) Branfill's observations in 1868+ on the polarisation of the corona. Mr. Proctor, indeed, in his book on the Sun, says that the Astronomer Royal did not consider them conclusive, but I have his official statement that he did so consider them, and an inquiry as to Mr. Proctor's authority leads me to think that Mr. Airy's meaning was mistaken. I think any one who reads the account in the original will feel that the plane of polarisation was satisfactorily determined. An observer in 1870 has said that he found the bands of Savart persistent. I have not now time to look up the reference, but he used, it seemed to me, the centre of the moon as the centre of rotation. Captain Branfill was careful not to do this, as his figures prove (page 25 of Report).

Now to the future. I have received from Government an inquiry as to recommendations to observers coming out. I am now suggesting, in addition to my own station at Dodabetta, that observers should be stationed at Kotagherry in the Nilgherries, at Manantoddy among the coffee districts to the west, and at Tirupur, close to Avenashy Road Station of the Madras Railway. Of these Manantoddy is the least accessible, but the whole will give a range of stations from 8,600 feet high down to the ordinary level of the plain country. More observers could be accommodated on the Nilgherries, where the weather, I am assured, is likely to be excellent. Of Ceylon I have not satisfactory accounts, nor of the west coast.

If these stations be adopted, I would suggest that, if possible, there should be a conference of observers. The possibility will depend on our leisure, which, probably, none of us can now

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British Mosses

NOT having noticed in the last number of NATURE, Oct. 12, any correction made by either the Rev. Mr. Berkeley or Dr. Dickie, of a statement made by the former gentleman in the previous number, Oct. 5, which, as it reads, is calculated to lead to error, if left unnoticed, I send you this note.

In the short paragraph at p. 446, "Notaris on Mosses," Mr. Berkeley, in correcting a previous omission having reference to the genus Habrodon, states that Conomitrium julianum had been sent to Dr. Dickie by Mr. Wilson from his district," Warrington. This being only one side of the truth, I take the liberty of supply ing the other side. Any person reading the paragraph as it stands would certainly suppose that this very elegant, and very remarkable moss was a native of the Warrington district, which it is not, nor of any other part of the British Isles that I am aware of. No doubt Dr. Dickie received fresh specimens of the moss from Mr. Wilson at Warrington, as I also did, but they were of foreign origin, and only cultivated by Mr. Wilson in his little conservatory at Warrington, where he had them placed in a largemouthed jar filled with water, in which condition I saw the plants during the month of October, 1870, on the occasion of the last visit I paid to my now departed friend.

I may fur.her remark that I had been led to suppose it was Dr. Schimper, of Strasburg, who first made known the genus Habrodon to be British. In the summer of 1865 he and the late Mr. Wilson paid me a visit at Dublin, and after leaving Ireland, Dr. Schimper accompanied a party to the Highlands of Scotland, on which excursion the Habrodon was discovered growing on trees near Killin, whence I have specimens from the party, which were collected on that occasion. Glasniven, Oct. 16

Corrections

D. MOORE

A PARENTHETICAL passage in my "note on the Cycloid" has been transposed. Instead of " (a luminous point for the nonce) the sun in the meridian," &c., it should have been "the sun (a luminous point for the nonce) in the meridian," &c.

In Mr. Abbott's paper on 7 Argus and its surrounding nebula there occurs the statement that I consider "an increased or decreased distance in space may account for the fluctuations of the nebula." I have never suggested such an explanation. What I have said is that the fluctuations, if real, would seem to suggest that the nebula has not those inconceivably vast dimensions which would correspond to the vast distance once assigned to it. My opinion was (and is), not that the nebula is nearer than it was formerly, but that it is nearer than it was formerly supposed to be. RICHD. A. PROCTOR

A Universal Atmosphere WILL you permit me to ask Mr. Mattieu Williams how, on his hypothesis, "that the atmosphere is universal, and that each planet attracts to itself an atmosphere in proportion to its mass," he accounts for the well-known fact that the moon shows no signs of an atmosphere sufficient to produce any indication of refraction during the occultations of a star?

I think Mr. Williams's book deserves far more attention than it has received, so I trust I shall be acquitted of any wish to indulge in carping criticism. JOHN BROWNING

III, Minories, October 10

The Temperature of the Sun

HAVING been absent from home I have but just seen Mr. Ericsson's article on the "Temperature of the Sun" in NATURE, (No. 101, p. 449. All who feel an interest in the subject must be indebted to Mr. Ericsson for the experimen tal evidence which he has contributed to the investigation, and for such further light as his ingenuity will doubtless enable him to throw upon it; but few, I think, will be inclined to admit that the reasoning advanced in his recent article justifies in any degree the inferences which he has there drawn.

At the outset of the inquiry it does not seem very likely that we shall gain much correct knowledge of the condition of the solar atmosphere by inquiring what that condition would be if it were replaced by a medium similar to the terrestrial atmosphere, and containing the same quantity of matter for corresponding areas of the spherical surface. If the case were otherwise it would be necessary to point out that Mr. Ericsson's numerical results are vitiated by his omission to consider that the volume of

a sphere varies as the cube of the radius, and therefore that on the data assumed by him the earth's atmosphere raised to the temperature of the solar surface, instead of attaining a height of 279,006 miles, would barely reach to one-twelfth of that limit. But I may further remark that the assumptions on which Mr. Ericsson's calculations are founded are open to many objections. It is far from certain that the direct proportion between the increase of volume of gases at constant pressure and the increase of temperature, holds good for an enormously high temperature such as prevails in the solar atmosphere, and it is certain that heat depends not solely or mainly on its temperature, but on its the resistance offered by that medium to the passage of radiant

chem cal-ie. its molecular-constitution.

It may further be noted that Mr. Ericsson's experiments on the diminution of heat emanating from a disc of incandescent iron, according to the angle at which its face is inclined to a fixed thermometer, do not justify similar conclusions with regard to heat emanating from a mass of incandescent gases or vapours. At the same time it may be regretted that Mr. Ericsson has not given fuller details respecting the experiments in question, which may give valuable results irrespective of the conclusions to which he has applied them. JOHN BALL

Flight of Butterflies

CAN you tell us where the yellow butterflies are going? About ten days since, while chatting with several gentlemen at the Jackson Sulphur Well about caterpillars, one of them remarked that the worm was about, for, says he, the yellow butterflies are all going east.

We thought at first he was telling us a "fish story", but soon became convinced that he knew whereof he spoke, for while we sat there a great number of bright-coloured, medium-sized butterflies came by us, all winging their way towards the rising sun.

Now, we do not think that this fly is related to the caterpillar, for the moth that lays the egg of that destructive worm is a very different fly; nevertheless it is a singular fact that they are all going east.

I have been at several different points since leaving Jackson, and at every place they fly the same way. Can you tell us whither they go? Perhaps if you will ask the question in your widely-circulated journal, some naturalist, or somebody over to the eastward, may tell us where they rest. Mobile, Sept. 6

ALA

[A similar fact will be found recorded in our "Notes" respecting the Urania leilus.-ED.]

Velocity of Sound in Coal

THIS is a very interesting subject, at least to those who have anything to do with coal mines. And yet I have not met with anything that points to it, nor any formula whereby it might be calculated. But perhaps this is a subject to which the attention of physicists has not been drawn. I have been told that blasting has been heard at the distance of 150 yards underground, and I have heard the signals of the colliers, i.e., by hitting the surface of the coal with one of their tools, at the distance of fifty or sixty yards, and have also heard the shouts of the men at the distance of fifteen yards; but I have never met any person who could give the velocity, nor seen any book on physics in which there is anything concerning it. But perhaps it is a very hard subject to deal with from the difference of the specific gravity of the coals, and also the different temperatures that we meet there. And if from these different causes it would be hard to find the real velocity, yet by calculating a velocity that might be rather theoretical at first, we might by degrees come nearer the truth. D. JOSEPH Ty Draw, Pontyfridd, Oct. 5

Prof, Newcomb and Mr. Stone

I AM obliged to Mr. Lynn for pointing out that the statement by "P. S." was contradicted. I had not been aware of this. It never occurred to me to doubt either the authorship or the authenticity of the statement. I cannot tell how it chanced that "W. T. L 's" response escaped my attention. Perhaps I never saw the January number of the Astronomical Register; or, perhaps, a variety of other reasons which would not interest your readers.

The only point of the least interest in the matter (if the matter has any interest at all) is the fact that Prof. Newcomb did not discuss the observations of 1769, as I had believed. I have already admitted this, and withdrawn those expressions of commendation which I had founded on the strongly worded letter of Prof. Smyth, so that I am rather at a loss to know what purpose Mr. Lynn had specially in view when he wrote his letter. thank him, however, as warmly as though I knew what he meant. RICHD. A. PROCTOR

TH

I

SCIENCE AT THE UNIVERSITIES HE following courses of lectures will be delivered at the University of Oxford in Natural and Physical Science during the ensuing term:-The Sedleian Professor of Natural Philosophy, the Rev. Bartholomew Price, M.A., will deliver a course of Lectures on Light, on Tuesdays, Thursdays, and Saturdays, at one o'clock, commencing October 19th, at the Lecture Room, Museum, Upper Corridor South. The Savilian Professor of Astronomy, the Rev. C. Pritchard, M.A., proposes to give two courses of lectures during the present term; the one on Astronomical Instruments, the other on the Lunar Theory. The Professor of Experimental Philosophy, R. B. Clifton, M.A., will give a course of Lectures on Experimental Optics, on Wednesdays and Fridays, at twelve o'clock, commencing October 20, at the Physical Laboratory, University Museum. The Physical Laboratory of the University will be open daily for instruction in Practical Physics, from ten to four o'clock, on and after Thursday, October 19. The Linacre Professor of Anatomy and Physiology, G. Rolleston, D.M., will lecture on Circulation and Respiration, on Tuesdays, Fridays, and Saturdays, at one o'clock, commencing October 20, at the Museum. The Professor proposes to form classes for Practical Instruction, as in former terms. Persons who join these classes will come to the lectures on Saturdays at one o'clock, and will also come to the Museum on three mornings in the week for study and demonstration, under the superintendence of Mr. Charles Robertson, the Demonstrator of Anatomy, and Mr. C. S. Taylor, of Merton College. The Hope Professor of Zoology, J. O. Westwood, M.A., will not lecture during the present term, being engaged in the classification of the Hope, Burchell, Bell, and other collections, at the New University Museum, where he will be happy to see gentlemen desirous of studying the Articulated Animals, daily, between 1 and 5 P.M. A course of lectures will be given on behalf of the Professor of Chemistry, by A. Vernon Harcourt, M.A., in continuation of the Professor's course, on Tuesdays and Saturdays, at eleven o'clock, commencing October 21, at the Museum. There will also be an Explanatory and Catechetical Lecture on Thursdays, at eleven o'clock, to commence on Thursday, October 26. The Laboratory of the University will be open daily for instruction in Practical Chemistry from 9 A.M. to 3 P.M., on and after Monday, October 16. The ordinary course of instruction in the laboratory includes those methods of Qualitative Analysis, a knowledge of which is required of candidates for honours in the School of Natural Science who make Chemistry their special subject. In addition to this two courses of instruction will be given in the Laboratory, the one on the Methods of Qualitative Analysis, the other a course of elementary practical instruction in Chemical Manipulation, intended for those commencing the study of Chemistry.

At Cambridge the following lectures in Natural Science will be delivered during Michaelmas Term in connection with Trinity, St. John's, and Sidney Sussex Colleges :On Electricity and Magnetism (for the Natural Sciences Tripos), by Mr. Trotter, Trinity College, on Mondays, Wednesdays, and Fridays, at 10, commencing Wednesday, October 18. On General Physics, Sound, and

Light (for the Natural Sciences Tripos 1972, and following years), by Mr. Trotter, Trinity College, on Tuesdays, Thursdays, and Saturdays, commencing Thursday, October 19. On Chemistry, by Mr. Main, St. John's College, on Mondays, Wednesdays, and Fridays, at 12, in St. John's College Laboratory, commencing Wednesday, October 18. Attendance on these lectures is recognised by the University for the certificate required by medical students previous to admission for the first examination for the degree of M.B. Instruction in Practical Chemistry will also be given. On Palæontology (the Protozoa and Coelenterata), by Mr. Bonney, St. John's College, on Mondays, Wednesdays, and Fridays, at 9, commencing Wednesday, October 18. On Geology (for the Natural Sciences Tripos, preliminary matter and Petrology), by Mr. Bonney, St. John's College, on Tuesdays and Thursdays, at 9, commencing Thursday, October 19. A course on Physical Geology will be given in the Lent Term, and on Stratigraphical Geology in the Easter Term. Papers will be given to questionists every Saturday at 11. On Botany, for the Natural Sciences Tripos, by Mr. Hicks, Sidney College, Tuesdays, Thursdays, and Saturdays, at 11, beginning on Tuesday, October 31. The lectures during this term will be on Vegetable Morphology. Mr. Hicks will also give examination papers in Botany to candidates for the next Natural Sciences Tripos on Mondays, at I P.M., beginning October 30. These examinations will be free to those who have attended the botanical lectures of the last term. On the Elements of Physiology, by the Trinity Prælector in Physiology (Dr. M. Foster), Mondays, Tuesdays, and Wednesdays, at II A.M.I., commencing Monday, October 23. A course of Elementary Practical Physiology, on Wednesdays and Thursdays, commencing Wednesday, October 25, at 2 P.M.

AN EXPLOSION (?) ON THE SUN*

ON the 7th of September, between half-past 12 and 2 P.M., there occurred an outburst of solar energy remarkable for its suddenness and violence. Just at noon the writer had been examining with the telespectroscope an enormous protuberance or hydrogen cloud on the eastern limb of the sun.

It had remained, with very little change since the preceding noon, a long, low, quiet-looking cloud, not very dense or brilliant, nor in any way remarkable except for its size. horizontal, andfloated above the chromosphere, with its It was made up mostly of filaments nearly lower surface at a height of some 15,000 miles, but was connected to it, as is usually the case, by three or four Lockyer compares such masses to a banyan grove. In vertical columns brighter and more active than the rest. length it measured 3′ 45′′, and in elevation about 2' to its upper surface, that is, since at the sun's distance, 1" equals 450 miles nearly, it was about 100,000 miles long by 54,000 high.

there was no indication of what was about to happen, At 12.30, when I was called away for a few minutes, except that one of the connecting stems at the southern extremity of the cloud had grown considerably brighter, and was curiously bent to one side; and near the base of another at the northern end a little brilliant lump had developed itself, shaped much like a summer thunder

head.

What was my surprise, then, on returning in less than whole thing had been literally blown to shreds by some half an hour (at 12.55), to find that in the meantime the inconceivable uprush from beneath. In place of the quiet cloud I had left, the air, if I may use the expression, was form filaments, each from 10" to 30" long by 2′′ or 3′′ wide filled with flying débris—a mass of detached vertical fusi

* From the Boston Journal of Chemistry, communicated by the author.

brighter and closer together where the pillars had formerly stood, and rapidly ascending.

When I first looked, some of them had already reached a height of nearly 4′ (100,000 miles), and while I watched them they rose with a motion almost perceptible to the eye, until in ten minutes (1.5) the uppermost were more than 200,000 miles above the solar surface. This was ascertained by careful measurement; the mean of three closely accordant determinations gave 7′ 49′′ as the extreme altitude attained, and I am particular in the statement because, so far as I know, chromospheric matter (red hydrogen in this case) has never before been observed at an altitude exceeding 5'. The velocity of ascent also, 166 miles per second, is considerably greater than anything hitherto recorded.

As the filaments rose they gradually faded away like a dissolving cloud, and at 1.15 only a few filmy wisps, with some brighter streamers low down near the chromosphere, remained to mark the place.

But in the meanwhile the little "thunder head," before alluded to, had grown and developed wonderfully into a mass of rolling and ever-changing flame, to speak according to appearances. First it was crowded down, as it were, along the solar surface; later it rose almost pyramidally 50,000 miles in height; then its summit was drawn out into long filaments and threads which were most curiously rolled backwards and downwards, like the volutes of an Ionic capital: and finally it faded away, and by 2.30 had vanished like the other.

The whole phenomenon suggested most forcibly the idea of an explosion under the great prominence, acting mainly upwards, but also in all directions outwards, and then after an interval followed by a corresponding inrush: and it seems far from impossible that the mysterious coronal streamers, if they turn out to be truly solar, as now seems likely, may find their origin and explanation in such events.

The same afternoon a portion of the chromosphere on the opposite (western) limb of the sun was for several hours in a state of unusual brilliancy and excitement, and showed in the spectrum more than 120 bright lines whose position was determined and catalogued-all that I had ever seen before, and some fifteen or twenty besides.

Whether the fine aurora borealis which succeeded in the evening was really the earth's response to this magnificent outburst of the sun is perhaps uncertain, but the coincidence is at least suggestive, and may easily become something more, if, as I somewhat confidently expect to learn, the Greenwich magnetic record indicates a disturbance precisely simultaneous with the solar explosion. C. A. YOUNG Dartmouth College, September 1871

THE KEA-PROGRESS OF DEVELOPMENT

A NOTICE of the development of a striking change in the habits of a bird may be considered by naturalists interesting enough to justify a brief record in your journal. The Kea (Nestor notabilis) may be seen and heard in certain localities amidst the wild scenery of the Southern Alps in the middle island of New Zealand, for it is not so rare as has been described. This fine bird belongs to one of our indigenous genera, an examination of its structure proves that it shares with the Kaka a claim to a position amongst the Trichoglossina or Brush-tongued Parrots; the under side of its thick tongue near the tip is fringed with papillæ, enabling it to collect the sweets of its favourite blossoms. Through how many years has this species been content to range over shrub-covered heights and rock-bound gullies, gathering its subsistence from the nectar of hardy flowers, from the drupes and berries of the dwarfed shrubs that contend with a rigorous climate, and press upwards almost to the snow line of our Alpine giants? To these food-resources may be added insects

found in the crevices of rocks, beneath the bark of trees, and its aliment not wholly vegetarian, yet such as called forth no display of boldness in order to procure a sufficient supply. This peaceful demeanour was observed under the ascendency of Moaic conservatism. The European has been the means of corrupting the simplicity of its ancient habits; the meat-gallows of the back-country squatters attracted the attention of our mountain-parrots in the winter season. To them they became points of interest in their wanderings, and furnished many a hearty meal torn from the dangling carcass as it swung in the frosty air; neither were the drying sheepskins, stretched on the rails of the stockyard, neglected. The Paneka has been destined to supply the enterprising Kea with a dainty only equalled perhaps by that which the epicurean African cuts warm from his bovine victim-our educated bird now tears his food from the back of the living sheep. From a local paper one learns that, for the last three years the sheep belonging to a settler "in the Wanaka district, (Otago) appeared afflicted with what was thought to be a new kind of disease; neighbours and shepherds were equally at a loss to account for it, having never seen anything of the kind before. The first appearance of this supposed disease is a patch of raw flesh on the loin of the sheep, about the size of a man's hand; from this matter continually runs down the side, taking the wool completely off the part it touches, and in many cases death is the result. At last a shepherd noticed one of the mountain parrots sticking to a sheep and pecking at a sore, and that the animal seemed unable to get rid of its tormentor. The runholder gave directions to his shepherds to keep watch on the parrots when mustering on the high ground; the result has been that during the present season when mustering high upon the ranges near the snow line, they saw several of the birds surrounding a sheep which was freshly bleeding from a small wound in the loin; on other sheep were noticed places where the Kea had begun to attack them, small pieces of wool having been picked out."

From the recent settlement of the country, it would be quite possible to date each step in the development of the destructiveness of the Kea, the gradual yet rapid change from the mild gentleness of a honey-eater, luxuriating amidst fragrant blossoms when the season was lapped in sunshine, or picking the berried fruits in the more sheltered gullies when winter had sternly crushed and hidden the vegetation of its summer haunts. Led, perhaps, to relish animal food from its partly insectivorous habits, its visits to the out-stations show something like the bold thievery of some of the Corvidae, whilst its attacks on sheep feeding on high ranges exhibit an amount of daring akin to the savage fierceness of a raptorial. Is the position of Nestor in our avifauna an anomalous one? A sucker of honey, devourer of fruit, destroyer of insects, render and tearer of flesh-will the difficulty be met by

classing our mountain bird as omnivorous, or is it to be considered as only one other instance in which system puzzles and hampers the field naturalist?

THOS. H. POTTS

ON A NEW FORM OF CLOUD*

THE accompanying figure on p. 490, represents a form of cloud which I have seen but twice in my life;* the first time about the commencement of June 1871, at five o'clock in the evening, at Washington, U.S.; the second at Beloit, Wisconsin, U.S., during The state of the same year, and at the same hour. the atmosphere presented similar meteorological conditions at both times. The appearances coincided with

* See my new classification of clouds with sixteen engravings in the Rural New Yorker, January 29, February 26, April 9, May 21, June 4 and 11. It will be reprinted in the Report of the Smithsonian Institution for

1870, with an historical introduction, in print now for the next number of the Annales Hydrographiques of Paris,

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a north-west storm passing slowly north of the city without bursting, and disappearing in the south-east. Great branched masses of cloud appeared suspended from a sheet of Pallio-Cirrus. Some resembled bunches of grapes (a), others stalactites (b) in a striking manner, and still others formed round balls (c) separated by the azure of the sky. These balls seemed to be formed of snow flakes, and approached the form of Cirro-Cumulus; one might say of masses of snow rolled upon themselves by the effect of electric currents developed during the storm. This was accompanied by thunder and lightning at Washington, and by lightning only at Beloit. d represents one of these balls detached, with two sorts of penumbra, darker in e and ƒ, and a streak at g, the rest whitish. Somebody at Beloit told me he had seen this form of cloud two or three times. A slightly brilliant aurora borealis was seen at Beloit the same evening. The night of its appearance at Washington no aurora was visible, but I do not know whether there may not have been one in other parts of

facts has been completed. Dr. M'Nab's article convinces me, as indeed is necessarily the case, that he has no conception either of the nature or of the extent of those facts. Were it otherwise, he would see at a glance how far his explanations are from accounting for them. He has given an exposition of a common process of exo. genous growth, which is true as far as it goes; but I can assure him that the modifications of that process, so far as we can infer from peculiarities of structure, have been much more varied in past geological ages than he is aware of. He is pleased to affirm two things which require proof: (1) that I have "been led away by the mere superficial resemblance of the parts;" and (2) that I have never tried to understand the homologies of these stems." To the first of these charges I plead not guilty; to the second I reply that I was trying to understand these things when he was a child at school. Whether or not I have succeeded remains to be seen, but as yet he has told me nothing new to me.

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In studying the relations of the several parts of a plant, we have to consider three things, of which Dr. M'Nab has mainly dwelt upon one. These are

1. The relative positions of the tissues.
2. The mode of their development.
3. The functions they have to perform.

a

f

e

B.0000

the United States. The same evening and the next day at Beloit the temperature fell several degrees. It is a general belief that the aurora borealis is followed by a decrease of temperature. We know that in higher strata of the air vapour of water floats constantly in the form of frozen needles, especially in the polar regions. It is not impossible that these ice needles may be drifted by the electric current which engenders the aurora borealis into lower latitudes, and thence towards lower strata of the atmosphere by the winds and storms. Hence the cooling of the air which is said to attend the ANDRÉ POEY

aurora.

EXOGENOUS STRUCTURES AMONGST THE
STEMS OF THE COAL MEASURES

THE perusal of Dr. M'Nab's reply to my short article
on the existence of an exogenous process of growth
amongst the cryptogamic stems of the coal measures,
confirms my previous conviction that the discussion of
the details of my proposition can lead to no beneficial
results until the publication of my large store of new

* See my Memoir on the Development of Electricity during the Aurora Borealis in the "Annuaire de la Société Météorologique de France," 1861, vol. ix. p. 42.

FIG. I

The first point where I shall differ from Dr. M'Nab is in supposing that a correspondence on the first of these clauses invariably pre-supposes a similar correspondence on the second. I shall have to show on a future occasion that Nature has attained the same end in more ways than one; and that she refuses to be shut up to that dichotomous arrangement pre-supposed by Dr. M'Nab; but ticular mode of growth upon which he rests his case. for the present I will limit my illustration to the par

If we take a perfect Stigmaria, we find its centre (a, Fig. 2, P. 491) to be occupied by an axis of ordinary cellular pårenchyma unmixed with any vascular tissue. This is surrounded by a ligneous or vascular cylinder (b) which, in its turn, is invested by a thick bark (c) consisting of a mixture of parenchyma and prosenchyma arranged in definite positions. The central axis differs in no respect whatever from the cellular piths of ordinary exogenous stems. The woody cylinder consists of vessels which, in the transverse section, are arranged in radiating lines (d) running from the pith to the bark; these lines are separated by intervening cellular tracts (e), which I, in common with Brongniart and Dr. Hooker, designate medullary rays. The radiating lines of vessels exhibit proofs of distinct interruptions to the process of growth, and afford clear evidence that the cylinder began as a thin ring of vessels surrounding the pith, and which grew, by successive concentric additions of vessels, to its peripheral surface where the cambium layer is found in ordinary exogens. We have here no trace of the limiting tissues of which Dr. M'Nab speaks; the growth has been free and prac

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