that such works as the present are calculated not to create Biologists, but to perpetuate a race of mere collectors and labellers-men whose highest aim is to gather "new" or "rare" species; who spend their holidays in accumulating specimens, sending those that are unfamiliar across the Channel for identification or naming. One of the results of the latter procedure is that the present work contains no less than 200 British species or varieties bearing Nylander's name as the author of their first description!

While, however, meagre attention has been thus bestowed upon the secondary reproductive organs, undue prominence is given to the action of potash and lime on the thallus and apothecia, and the reaction of iodine with the hymenial gelatine; phenomena that are so uncertain and inconstant that they vary even in the same individual under different circumstances. We would not exclude chemical or any natural characters from the definition of species; but the present work seems to us to furnish ample illustration of the danger of making use of secondary, trivial, inconstant characters as a basis for classification (e.g. the genus Cladonia.)

The localities of growth are satisfactory so far as they go; but they are utterly inadequate as representing the distribution of species in either of the three kingdoms. In order to specify, with at all adequate fulness, the diversity of locality occupied in England, Scotland, and Ireland respectively by the species enumerated, Mr. Leighton must have examined for himself the contents of all the Lichen-Herbaria in these kingdoms; and, though the said herbaria are neither numerous nor large, compared with those of flowering plants, such a labour is obviously impossible for any one man of average leisure and opportunities.

There is no Tabular Summary showing the numerical richness of the British Lichen-Flora; an omission, it may be, of minor importance, but still of importance, inasmuch as it is always interesting to "take stock" occasionally of the rate of progress of the additions that are being made to a national Sub-Flora. Basing our calculations on the data supplied by the present work, we find a total of 73 genera and no less than 781 species; whereas only last year in his enumeration, Crombie (p. 124), gave the whole number of British Lichens then known as 658, the difference apparently representing, or consisting of, so-called new species. Of the host of these new species added of late years to our Lichen Flora, perhaps not above onefifth will survive in that "struggle for existence," to which they will sooner or later have to submit at the hands of the philosophic botanist. A large proportion will doubtless be found to consist of mere forms of common, protean, widely distributed species-forms that neither require nor deserve separate nomenclature and rank.

We have not exhausted the list of blemishes in the

book before us. But to notice all the errors in matters of detail; all those points on which other lichenologists are likely to take grave exception to his views; all the faults in typography or otherwise, would extend and expand this review into a Treatise on the Classification of Lichens; for it would necessarily deal with certain features of that Nylanderian system, which Mr. Leighton follows in his present work.

With all the aids the author gives the student, it will,

we fear, be impossible for the latter to identify the majority of the less common and familiar species without reference to authentic specimens named by Mr. Leighton himself. The work is so elaborate and complex, the principles and practice of classification adopted in it are so puzzling, that candidly confess our own general impression to be one of increasing bewilderment, and of growing indisposition to attempt the identification or nomenclature of Lichens at all! We hesitate not to avow our own preference for studies on the Biology of the common economical species, such as those which at present are called Cladonia rangiferina, Usnea tarbata, Ramalina calicaris, Parmelia saxatilis, Roccella tinctoria, or Lecanora tartarea.

On the whole, however, the "Lichen-Flora of Great Britain" is a work that should find a place in every public botanical library in the three kingdoms, as well as in the private libraries of all students of the extremely puzzling cryptogamic family of which it treats.

W. LAUDER LINDSAY

OUR BOOK SHELF

A Complete Course of Problems in Practical and Plane Geometry, adapted for the Use of Students preparing for the Examinations, &c. By John William Palliser, Second Master and Lecturer of the Leeds School of Art and Science. (London: Simpkin and Marshall) A NEW class-book on Practical Geometry commends itself to our attention. Mr. John Palliser, of the Leeds School of Art and Science, has produced one of those educational works which a demand created by Government examinations has recently brought to our aid. Reserving our opinion as to the final tendency of an epidemic for what are called practical results, we must, in justice, say that this class-book of Mr. Palliser's is the very thing for cheapness, conciseness, comprehensiveness, to rapidly possess the student with a ready-handed ability to answer all demands of the examiner. The work is not encumbered with demonstration, for this, in view of the proposed end, would be out of place; it is a laboratory of experi conceivable polygons within the compass of a single mental formulæ. We have a recipe for constructing all circle, for drawing lines to invisible points, and for trisecting the most obdurate angles by the magic of a slip of paper. Faith is all that is demanded of the student, faith in the formulæ before him, and industry to get them by heart Not troubled with the Why, he has only to remember the How; but he must be careful, exact, and neat-handed; and this, if not mental training, is next of kin to it. The arrange ment of the book is generally good, the style concise in the extreme, the letter-press wonderful at the price, and the diagrams, with their faint, dark, or dotted lines, are highly effective and intelligible, not less so from the fact of the lettering being (what we very seldom find it) correct.

To examine in detail the 220 problems of Mr. Palli. ser's book is more than we can just now undertake; but so far as we have dipt into them there is little to complain of, considering that the work is merely practical. The style, we have said, is concise; but (if we might venture a criticism on a point where most geometers are more guilty than Mr. Palliser) it would lose nothing in intelligibility if the nominative case were less frequently preceded by a multitude of perplexing conditions which really have to be neglected by the learner till the said nominative is reached, and then returned to lastly in that natural order of thought which geometers have a fancy for inverting. call the author's serious attention to Problem 13, which, Whilst taking these minor exceptions, we must not omit to whether we consult the diagram or the letter-press, is wholly fallacious. Such a construction will not effect the

LETTERS TO THE EDITOR

[The Editor does not hold himself responsible for opinions expressed by his Correspondents. No notice is taken of anonymous communications.]

Geometry at Oxford

IN the last number of NATURE Mr. Proctor remarks that "no one who considers carefully the mathematical course at either University, can believe that it tends either to form geometricians or to foster geometrical taste."

With regard to Oxford, I think it is only fair that some qualification should be offered to this conclusion. In Cambridge, candidates for mathematical honours have to run their race in a course clearly marked out for them, and loss of place is naturally the result of individual vagaries. But in Oxford the order of merit is not carried further than distribution into classes, and I do not believe there is anything to prevent a skilful geometrician finding himself in the first class with those who put their trust most in analytical methods.

I cannot pretend to much geometrical capacity, but I know something of Oxford mathematical teaching. Speaking for myself, the fascinating lectures of the present Savilian Professor of Geometry will never cease to hold perhaps the most prominent place in my recollections of university work. It is quite true that I remember conversing with a college tutor who was rather doubtful about modern geometrical methods, and seemed disposed to look upon these lectures as dangerous." He was a great stickler, however, for "legitimacy," thinking it wrong, for example, to import differential notation into analytical geometry; but I do not think he had a large following amongst younger Oxford men. I certainly did not find, in reading with some of them, that geometry was at all in disfavour. I have often had neat geometrical solutions pointed out to me of problems where other methods proved cumbrous or uninteresting; and conversely I have found geometrical short cuts were far from objected to. On the whole, the characteristic feature of the Oxford examination system (most marked in the Natural Science School, but making itself felt in all the others) being to encourage a student after reaching a certain point in general reading to make himself strong in some particular branch of his subject, I believe special attention to geometrical methods would pay very well. Oct. 13 W. T. THISELTON DYER

Elementary Geometry

YOUR 'correspondent, "A Father," has in view a very desirable object-to teach a young child geometry-but I fear that he is likely to miss altogether the path by which it may be reached. His principle, that "a child must of necessity commit to memory much that he does not comprehend," appears to me to be totally erroneous, and not entitled to be called a fact. To this time-hallowed principle it is due that a large proportion of all who go to school learn nothing at all, while those more successful learn with little improvement of their faculties. It is a convenient principle which allows the title of teacher to be assumed by those who only hear lessons. Children labour under this difficulty that they learn only through language, which is to them a misty medium, particularly when the matter set before them is in any degree novel or abstruse, and no pains are taken to clear up the obscurity of new expressions. Children know nothing of abstraction, and learn to generalise from experience, not from words. Committing to memory what is not understood is a disagreeable task; begetting a hatred of learning, and causing many to believe that they want the special faculty required for the task set before them. The art of teaching the young ought to be the art of enabling them to comprehend, and memory ought to be strengthened not by drudgery but by being founded on understanding and by the rational connection of ideas.

Now geometry is the science of figure; it theorises reality, and the truth of every proposition in it may be made apparent to the

what is meant by a parallelogram, and he will perceive its properties, viz., that its opposite sides and angles are equal; that it he acquires only a cloud of words, on which his mind never is bisected by the diagonal, &c. But if he learns all this by rote, dwells. Propositions touching abstractions and generalisations can never be understood by the young without abundant illustration. When a geometrical truth is made apparent to the senses, when seen as a fact and fully understood, the language in which it is expressed having no longer a dim and flickering light, is easily learned and remembered, and the learner listens with pleasure to the discussion of the why and wherefore.

It is not enough for a child to learn by rote the definition of an angle. He ought to be shown how it is measured by a circle; and by circles of different sizes. In short, he ought to be taught what words alone will not teach him, that an angle is only the divergence of two lines. Let us now come to the important theorem that the three angles of any triangle are equal to two right angles (Euclid i. 32). Cut a paper triangle, mark the angles, then separate them by dividing the triangle and place the three angles together. They will lie together, filling one side of a right line, nd thus be equal to two right angles. Let the learner test the theorem with triangles of himself of its generality, and then, every possible shape to convince fully understanding what it means, he will also understand the lan

guage in which it is proved.

a

It is a mistake to decry the use of symbols. They enable us to get rid of the wilderness of words, which form a great impediment in mathematical reasoning. Ordinary language can never group complex relations for comparison so compactly as to bring them within the grasp of the understanding. When we would compare objects, we place them close together, side by side. But the features and l'neaments of objects described in language are too widely scattered to be kept steadily in view. It is easier to learn the use of symbols than to commit to memory what is not understood. Those who would learn mathematics without symbols can advance but a little way.

Neither is there any good reason for rejecting the second book of Euclid, though it certainly may be much abridged. The rela tions of whole and parts, sum and difference are easily exhibited, and an acquaintance with them is of great value to arithmeticians. Let us take for example the following propositions : "The squares (A and B) of any two lines (or numbers) are equal to double the rectangle under those lines (R and R, or the product in case of numbers) and the square of their difference D."

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.

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 ede, and place them in the positions of bm f and ƒne, 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 a 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.

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 te 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 deter mined. An observer in 1870 has said that he found the banda of Savart persistent. I have not now time to look up the reference, but he used, it seemed to me, the centre of the mo 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 wil 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. Óf 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

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 supplying 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 further 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 ʼn 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 experimental 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 the resistance offered by that medium to the passage of radiant heat depends not solely or mainly on its temperature, but on its chemical-i.c. 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 butter. flies 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

[A similar fact will be found recorded in our specting the Urania leilus.—ED.]

Velocity of Sound in Coal

ALA

"Notes" re

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 theoretical at first, we might by degrees come nearer the truth. real velocity, yet by calculating a velocity that might be rather 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

I

SCIENCE AT THE UNIVERSITIES THE 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 Paleontology (the Protozoa and Colenterata), 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 11 A..., 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*

ΟΝ N 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 limb of the sun. enormous protuberance or hydrogen cloud on the eastern

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 horizontal, andfloated above the chromosphere, with its its size. 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 half an hour (at 12.55), to find that in the meantime the whole thing had been literally blown to shreds by some 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 authen