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THURSDAY, OCTOBER 26, 1871

SCIENCE IN AMERICA Proceedings of the Essex Institute. Vols. I.-V. Proceedings and Communications of the Essex Institute. Vol. VI. Bulletin of the Essex Institute. Vols. I. and II. (Salem, Massachusetts. Published by the Essex Institute, 1856-1871.)

horticulture and agriculture in connection with the general library.

From 1848 to 1866 the Essex Institute published five volumes of "Proceedings," containing reports of papers read before the Institute on the various subjects included in the programme. Among the more important papers contained in these volumes may be mentioned the following-List of Infusoria found chiefly in the neighbourhood of Salem, by Thomas Cole (1853); Catalogue of the Birds of Essex County, by F. W. Putnam, 235 species

WE have, on various occasions, alluded to the large (1856); Account of the life, character, &c., of the Rev.

amount of encouragement to the pursuit of science afforded by the governing powers of the United States, both by the Central Federal Government at Washington, and by those of the individual States. The sums of money voted for such purposes by our American relations would make the hair of our economical Govern

ment officials in this country stand on end, and would be certain to provoke angry comment in our House of Commons; while the number of scientific men paid for carrying on investigations and preparing reports on various subjects of great practical value for the welfare of the country, would almost bear comparison with the number we pay for doing nothing or for obstructing all rational improvements.

When men of culture and science in this country attempt to advocate the claims of Science to national support from the Government, one of the arguments most relied on by their opponents is that such a course would have the effect of checking all scientific enterprise and research that was not paid for by the State. We should like these objectors to look over the publications now lying before us; and we think, if they were able to derive any lesson from it, it might have a tendency to modify their opinion.

New England is acknowledged to be the most highly educated portion of the United States, and among the New England States none occupies a more honourable position than Massachusetts for its high standard of cultivation, and for the public-spirited manner in which its citizens tax themselves for the support of education and the spread of knowledge, scientific and otherwise. The early New England settlers had a loving habit of perpetuating in their new settlements the names of familiar places in the old country, and thus we find one of its counties called Essex, with an area about equal to that of our Middlesex, possessing a scientific institute located in the thriving town of Salem. A sketch of the history of the Essex Institute since its foundation may convey some idea of the manner in which voluntary scientific effort is carried on in Massachusetts.

The Essex Institute was formed in 1847 by the union of the Essex Historical and the Essex County Natural History Societies; and the Institute, thus organised, consisted of three departments-the historical, having for its object the collection and preservation of whatever relates to the topography, antiquities, and civil and ecclesiastical history of Essex County; the natural history, for the formation of a cabinet of natural productions in general, and more particularly of those in the county, and for a library of standard works on the natural sciences; and the horticultural, for promoting a taste for the cultivation of choice fruits and flowers, and for collecting works on

VOL. IV.

Samuel Parris, of Salem Village, and of his connection with the Witchcraft delusion of 1692, by Samuel P. Fowler (1856), reminding one exceedingly of a history that will probably one day be written of certain similar delusions not unknown in our own day; On Indian Relics from Marbleshead (1857); Noticeable traits of the Flora of Nahant, by C. M. Tracy (1858); On the changes produced by Civilisation in the habits of our common Birds, by S. D. Fowler (1860); Catalogue of the Birds found at Norway, Oxford County, Maine, by A. P. Verrill (1862); Report of the Army Worm (Leucania unipuncta, Ham.), by Carleton A. Shurtleff (1862); Catalogue of Birds found at Springfield, Mass., with Notes on their migrations, habits, &c., by J. A. Allen (1864); The Humble Bees of New England and their Parasites, by A. S. Packard, jun. (1864); A classification of Mollusca, based on the principle of Cephalisation, by Edward S. Morse (1865); Synopsis of the Polyps and Corals of the North Pacific Exploring Expedition under Commodore C. Ringgold and Captain John Rodgers, U.S.N., from 1853 to 1856, by A. P. Verrill (1805-06); Flora of the Hawaian Islands, by Horace Mann (1866).

From 1867 the Transactions of the Institute have been published in a slightly different form, under the title of "Proceedings and Communications of the Essex Institute," its contents consisting to a considerable extent of continuations of some of the elaborate and important papers commenced in the earlier volumes, especially of Prof. Verrill's "Synopsis of the Corals and Polyps of the North Pacific Exploring Expedition," and of the "Flora Hawaii," by Mr. Horace Mann, whose carly death was an irreparable loss to American botanists. There are also a number of papers by Mr. A. S. Packard, whose services to embryology are so well known, and the very valuable contribution by Dr. Elliott Coues, " Catalogue of Birds of North America contained in the Museum of the Essex Institute; with which is incorporated a list of the Birds of New England, with brief critical and field notes." The following quotation from this paper will interest ornithological readers :-"Within the area of New England are represented portions of two fauna, the Canadian and Alleghanian, which differ in many respects from each other. There seems to be a natural dividing line between the birds of Massachusetts and Southern New England generally, and those of the more northern portions of the Eastern States. Numerous species which enter New England in spring, to breed there, do not proceed, as a general rule, farther north than Massachusetts, and many others, properly to be regarded as stragglers from the south in summer and early autumn, are rarely, if ever, found beyond the latitude of this State. In like manner, many of the regular winter visitants of Maine are of rare

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and only occasional occurrence, and are not found at all much farther south. Again, many species hardly known in Massachusetts and southward, except as migratory species passing through in spring and autumn, are in Maine regular summer visitants, breeding abundantly. Other minor differences, resulting from latitude and physical geography, will readily be brought to mind by attentive consideration of the subject, and therefore need not be here detailed. It will be evident that a due regard for these important points has necessitated, in the case of almost every species in the list, remarks elucidative of the special part it plays in the composition of the avifauna." The later numbers, especially of the Proceedings, are illustrated by admirably executed lithographs illustrative of the natural history pages, and a considerable amount of space is occupied by reports of the Field meetings of the members. It is interesting to read that the idea of these excursions, which have been productive of such valuable practical result, originated from a perusal of the Transactions of the Berwickshire Naturalists' Club.

While thus affording a medium for the publication of papers of sterling scientific value, the Essex Institute has not been unmindful of the no less imperative duty of scientific bodies, that of promoting a taste for science among the educated but unscientific public. We in this country have perhaps erred in too much ignoring the profanum vulgus. It becomes, however, yearly more and more manifest that science must be no esoteric religion, but that it must grasp, in its all-including embrace every section of the community. It is doubtful, indeed, which class of scientific men deserves best of the republic, those who devote the whole of their time to actual work in the laboratory or the dissecting-room; or those who of the riches of their knowledge impart to the ignorant crowd in the lecture-room or by the popular treatise. With the names of the former will doubtless be connected the most important discoveries of the age; the latter will have the satisfaction of knowing that they have done their part towards making science really popular, towards spreading its blessings among the masses. The danger is when the instruction of the public is undertaken by those who have not practically made themselves masters of the mysteries which they presume to communicate to others.

Commencing with January 1869, the issue was commenced, in addition to the publications named above, of the "Bulletin of the Essex Institute," the object being to give to the public such portions of communications made to the Institute as are of popular interest. We find here, in language intelligible to non-scientific readers, reports of such proceedings and papers read at meetings of the Institute, in Natural History, Philology, and History, as are likely to interest the inhabitants of the county generally; and we look upon this as not the least valuable of its publications.

An interesting publication in connection with the Essex Institute is "The Naturalists' Directory," which is intended, when complete, to form a list of the addresses of the workers in each department of science all over the world. If ever the proposed union of our scientific societies is effected, we may get something of the kind in this

country.

The above account of the Proceedings of the Essex Institute since its foundation may serve to show the zeal

displayed by workers in Natural History in the United States, and may also be useful in pointing out some hitherto unrecognised fields of usefulness to similar bodies at home.

OUR BOOK SHELF

Contributions to the Flora of Mentone, and to a Winter Flora of the Riviera, including the Coast from Marseilles to Genoa. By J. Traherne Moggridge, F.L.S. 100 coloured plates. (London: L. Reeve and Co., 1871.) MR. MCGGRIDGE has collected in this splendid volume drawings and descriptions of one hundred of the most striking plants of the Mediterranean coast of France. We have no preface to inform us on what principles the selection has been made, nor are they self-evident. But few of the species are new, though some of them are doubtful plants of which precise characters were much wanted. Mr. Moggridge is well known to English botanists as an accurate and careful observer, who has paid great attention to the botany of this district; and he has here produced a volume which is not only a useful contribution to science, but is surpassed by few that we know as a livre de luxe to lie on the drawing room table. The illustrations are beautifully drawn by the author himself, and are exquisitely coloured. Mr. Moggridge has made himself thoroughly acquainted with the beautiful but difficult species or varieties of Orchis of the south of France related to our Bee-orchis. It is remarkable that, while on our chalk-hills the bee and fly orchis, Ophrys apifera and muscifera, remain perfectly distinct, in the south of Europe they approximate to one another by innumerable intermediate forms, which may all be considered as varieties of Linnæus's O. insectifera. These are here worked out with great care, and we have plates of a number of the most interesting forms. A. W. B. Zeitschrift der österreichischen Gesellschaft für Meteorologie. Redigirt von Dr. C. Jelinek und Dr. J. Hann, v. Band, mit 3 lithographirten Tafeln, pp. 644; vi. Band, pp. 1—224 (Wien, 1870-71.)

THE fifth volume of the Journal of the Austrian Meteorological Society, published fortnightly, and extending in one year to 644 octavo pages, shows at once the extraordinary energy with which this society conducts its operations, and the high estimation in which meteorology is held in Austria. What strikes one as the most remarkable feature of this periodical is the broad and catholic spirit in which the science is treated. Whilst the articles are mostly written by members of the society, the pages of the journal are open to meteorologists in all parts of the globe. Reprints or abstracts, accompanied where necessary with tabular matter, of the more important meteorological papers which have been published in other journals, appear from time to time. A few of the more important of these are the following, viz :Dove's "Non-periodic Changes of the Distribution of Temperature over the Earth's Surface," D. Milne Home's "Increasing the Supply of Spring Water at Malta, and Improving the Climate of the Island," Glaisher's "Temperature of the Air at Different Heights," Buchan's "Mean Pressure and Prevailing Winds over the Globe," Wojeikof's

Mean Temperature of Russia," Raulin's "Rainfall of Algiers," Rayet's "Climates of the Isthmus of Suez," Jelinek's "Distribution of Thunderstorms in Austria," Petermann's "Monogram on the Gulf-Stream," Mohn's "Temperature of the Sea," and Angus Smith's "ComThe abstracts are not position of the Atmosphere." bald productions, but ably written and readable articles. Another admirable feature is the papers on the climates of places in different parts of the globe, by Dr. Hann, one of the editors and unquestionably one of the greatest

of the younger meteorologists on the Continent. These papers are accompanied by tables giving the mean pressure, temperature, humidity, rainfall, wind, and cloud; and their very great value will be recognised when it is stated that they embrace places whose meteorology was little, if at all known, such as Rio Janeiro, Parana, Mendoza, Monte Video, Buenos-Ayres, Punta-Arenas, Puerto Montt, Santiago, Valdivia, Valparaiso, Serena, Copiapo, and Lima, in South America; Bagdad and Samaua in Mesopotamia; Kuldscha in West China; St. Anna, near Manila, Philippine Islands; and Said, Ismailia, and Suez. Since broad and just views of the atmosphere and its move ments can be attained only through the accumulation of such facts and an intelligent discussion of them, our best thanks are due to the Austrian meteorologists for these invaluable contributions. If meteorology were prosecuted more in this spirit than, unhappily, has been the case, it would be marred by fewer crude and hastily-formed theories; and particularly inquiries into local climates and weather over limited portions of the earth's surface would be conducted on sounder principles, and be productive of results which could be accepted as solid contributions to science. We heartily recommend this journal, especially since in this country we have nothing to compare with it, no periodical which so well puts meteorologists and physicists au courant with this rapidly-advancing science.

Das Leben der Erde: Blicke in ihre Geschichte, nebst Darstellung der wichtigsten und interessantesten Fragen ihres Natur- und Kultur-lebens. Ein Volksbuch von A. Hummel. (Leipzig: F. Fleischer; London: Williams and Norgate, 1870.)

IT is always a question of doubtful expediency whether it is wise to compress into one work by one writer a complete history of Nature, even in a popular treatise. This has been attempted by Herr Hummel in this volume of 424 pages, and, as far as such an attempt can succeed, not unsuccessfully. We have first a glimpse of the origin of the earth, and of its relations to the solar system. Then follows a chapter on the physical geography of the land, describing the main physical features of the solid crust of the globe. Next we have a treatise on water, and the part it has played in the formation of the existing surface of the earth. To this succeeds a chapter on the atmosphere and its phenomena. In conclusion we have a general sketch of the vegetation of the earth, and of the forms of animal life, in which the author declares against the Darwinian theory of the origin of species. Written occasionally in the inflated language in which continental popular writers too much indulge, the work is, nevertheless, a good one to put in the hands of young people with the double purpose of giving them some knowledge of natural science and of German. It was published on the hundredth birthday of Alexander von Humboldt, as a tribute to the memory of the great naturalist.

LETTERS TO THE EDITOR

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

The Sun's Parallax

Is there nobody who will perform an act of justice, and ask those who seem to have never known or to have forgotten my doings, to be kind enough not to deprive me of my just claims? When, A.D. 1857, my old method of determining the sun's parallax was again publicly proposed, I thought it somewhat strange, and wondered what could be the reason that it should be treated as if it were some new and not a very old acquaintance of Science. When, some time later, a stir was made about what was represented as a new method of investigating the motion of the solar system in space, and, instead of a new, there was brought forward an old acquaintance (known to Science

since the times of your grandfathers), only dressed anew, and engaged to perform some truly " astounding" antics, I wondered indeed that no friendly hand should have prevented such an exhibition, but I also comprehended the true state of affairs. And since then I have had to shrug my ghostly shoulders so often Science, and your strange opinions, and your queer notions of when learning further news about your curious knowledge of honour, and justice, and fairness, that I have long ceased to wonder at anything some of you may say or do. However, as it is only right that I should be allowed to retain what belongs to me, and as nobody appears to remember my claims, you will probably raise no objection, if I, myself, enlighten you a little, and remind you how, A. D. 1672, I determined the sun's parallax. Read in the History of my Life (Baily's Account, &c. p. 32):

"Whilst I was inquiring for the planets' appulses to the fixed stars by the help of Hecker's ephemerides, I found that, in September 1672, the planet Mars, then newly past his perihe lion and opposition to the sun, would pass amongst three contiguous fixed stars in the water of Aquarius; and that by reason he was then very near the earth, this would be the most convenient opportunity that would be afforded of many years for determining his, and consequently the sun's, horizontal parallax. I drew up a monitum of this appearance, and sent it with a letter to Mr. Oldenburg, who printed it in his Transactions, No. 86, August 19th, 1672, having before sent my admonition into France, where the gentlemen of their Academy took care to have it observed in several places. My father's affairs caused me to take a journey into Lancashire the very day I had designed to begin my observations, but God's Providence so ordered it that they gave me an opportunity to visit Townley, where I was kindly received and entertained by Mr. Townley, with whose instruments I saw Mars near the middlemost of the three adjacent fixed stars. My stay in Lancashire was short. At my return from thence I took his distances from two of them at distant times of the night. Whence I determined his parallax then 25", equal to his visible diameter; which, therefore, must parallax not more than 10". This I gave notice of in the Tran be its constant measure, and, consequently, the sun's horizontal sactions, No. 96; and the French soon after declared that from their observations they had found the same. Whether they will give you such exactness I leave to those who are skilled in these things to determine."

This extract is, I hope, sufficient, and I will leave it to you to search further. Perhaps you may consider my language a little quaint, but then, remember, I lived two centuries ago.

Now, the planet Mars performs 109 sidereal revolutions in 205 sidereal years and 3 days, so that its appearance in the year 1877 will not be very different from what it was in 1672. Accordingly I enjoin you to make then the most of your oppor tunity, and do your best to prove the goodness of my old method, and I wish you thorough success. And when you watch the planet pass amongst the stars in the water of Aquarius, you will, perhaps, remember with kindly feelings an old astronomer, who in life had to endure great injustice and sore trials, and will bless and honour his memory.

Walhalla

THE GHOST OF JOHN FLAMSTEED, M.R.

The Marseilles Meteorite

IT will probably occur to most of your readers, as it immedi diately suggested itself to me, on reading in your journal of the 5th inst. a description from Les Mondes of a remarkable meteorite ob-erved at Marseilles by M. Coggia, on the 1st of August last, that the bright object having an apparent diameter, at first of about 15', and at last of a little over 4', whose uncertain course was noted for eighteen minutes by the stars, was really nothing more extraordinary than a fire-ball on; or it may, possibly, have been some description of brighter signal-light. The planet Saturn, and the other stars named in the description, were all at the low altitude above the horizon, at which a fi e-balloon, and other bright signal-lights of ordinary size, floating at an ordinary height in the air, would have about the apparent diameter of the "meteorite." Its apparent diminution in size was, also, perhaps, either the effect of its increasing distance, or of its gradually fading light. After alternately remaining stationary, and changing its apparent course two or three times, it at last fell rapidly in a perpendicular direction. The burning tow, or other inflamed substance with which it was inflated, appears to have detached itself from, or, it may be, to have set fire to the balloon, since it

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Exogenous Structure in Coal-Plants PROF. WILLIAMSON criticises my want of certainty with respect to the exogenous mode of growth of extinct Lycopodiaceæ. But surely his reference to the Dixonfold trees does not prove more than that the diameter of their stems was greater near the roots than higher up. The same thing is true of many palms, but I think Prof. Williamson would be the last person to say that it was evidence of their being exogenous. Nevertheless, as I have already said, I am inclined to think that Prof. Williamson is right in supposing that the stems of extinct arborescent Lycopodiaceæ increased in thickness, although I do not see my way to asserting off hand that this was the case. Even admitting, with all Prof. Williamson's confidence, that it was so, I can see no classificatory value in the fact to justify overriding reproductive characters in his new classification.

I said in my former letter (and the argument still appears to me a good one) that this increase was in any case "nothing more than an adjustment to an arborescent habit dropped when the arborescent habit was lost." Prof. Williamson finds some difficulty in understanding this, and believes me to imply "that these exogenous conditions were merely adventitious growths assumed for a season and thrown off at the earliest opportunity; that they had no true affinity with the plants in which they were found." He confesses that he sees no ground for so remarkable a conclusion, and I may certainly say that as far as I comprehend it, neither do I..

What I did mean to imply was, that in comparing the stems

of existing with those of extinct Lycopodiacea, allowance must be made for such adaptations of structure as would be likely to be correlated with enormous size. To make the matter clearer by an illustration :-Suppose we compare a nearly allied woody and herbaceous plant, say a lupin and a laburnum, we shall find in their stems (both "exogens ") the same kind of differences as exist between the stem of a herbaceous Selaginella and that of the nearly allied arborescent Lepidodendron. The lupin may have had arborescent ancestors; if so, it has dropped all such adaptations of the structure of its stem to an arborescent habit as we find existing in laburnum. Assuming (what is of course only an assumption) that Selaginella is a descendant of Lepidodendron or its allies, the parsimony of nature has also suppressed in it all those peculiarities of stem structure which were merely correlated with vast size, and in Selaginella and recent Lycopodiaceae we have the residuum. In Isoetes, which is only a few inches high, there is a kind of lingering reminiscence of circumferential growth.

Prof. Williamson says that "herbs if they belong to the exogenous group are as truly exogenous in their type as the most gigantic trees of the same class. Size has nothing to do with the matter." With these statements I altogether disagree. I look upon the terms exogen, endogen, and acrogen as altogether obsolete from a classificatory point of view. Mohl pointed this out more than twenty years ago. Compare the following remarks from one of his memoirs with Prof. Williamson's: "The course of the vascular bundles in the palm stem and in the oneyear-old shoot of the dicotyledons is exactly similar, and the conception of a different mode of growth, and the division of plants into endogens and exogens formed on it is altogether opposed to nature.

Size, in fact, has everything to do with the matter. It is the persistent growth of the ends of the branches which makes the strengthening of the main stem by circumferential growth a mechanical necessity. Palms not being branched do not require the voluminous stem of an oak, and they exhibit on an enlarged scale only the structure of a one-year-old herbaceous shoot. But in the dragon-tree of Teneriffe an "endogen," which becomes extensively branched, there is a true circumferential growth of the main stem, which increases pari passu with the development of the branches. All herbaceous stems, on the contrary, among flowering plants, whether belonging to the exogenous or endogenous group, have practically the same type of structure. Where is the exogenous type in the stem of the common artichoke, or in Ferula communis, figured by De Candolle in his "Organographie Végétale," pl. 3, fig. 3, "pour montrer à quel point elle simule les tiges de monocotyledones" (endogens)?

I think these remarks make it plain that circumferential (which is a preferable expression to exogenous) growth in stems is simply a necessary accompaniment of a branched arborescent habit. As far as the affinities of plants are concerned, it is purely accidental and of no classificatory value. Lupinus being herbaceous and Laburnum arborescent does not prevent their being placed in the same tribe of a natural family. Since Mohl has shown that one-year-old (herbaceous) stems conform to the endogenous type, while such woody stems as Laburnum possesses are of course exogenous, it is clear that Prof. Williamson's views would overthrow all the work of modern systematists, and bring us back, as I pointed out in my former letter, to the primitive division of plants into trees and herbs (not trees and shrubs as Prof. Williamson makes me say).

The interpretation of the actual structure of the stems of the extinct Lycopodiaceae is of course another matter. Prof. Williamson illustrated his views at Edinburgh by referring to Lepidodendron selaginoides; every botanist who took part in the discussion, however, objected to his explanation. It may be true that this is only one form of such stems, but of course I can hardly be expected to be acquainted with the unpublished material which Prof. Williamson still has in hand. There is, I think myself, good reason for believing that Lepidodendron, Sigillaria, and Ulodendron all belong to a common type of stem structure; differences in fragments of different age of growth must be expected and allowed for. Of course, as I do not accept the existence of a pith in these plants, the pith or medullary rays must be rejected as well. Mr. Carruthers has shown, I think, conclusive reasons for disagreeing with Dr. Hooker with respect to the spaces which he identified with those structures. already familiar with the view of these s ems taken by Prof. Williamson in his last paper. Those who are interested in the matter must judge for themselves who is right.

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inst., and especially those who have kept a record of similar exhibitions, may have remarked the frequency with which the phenomena have occurred about the same epoch, viz., from February 15 to February 23. Some of the most brilliant that have occurred at this period during the last century are the fol1848 February 20

This communication has run on to so great a length that I am unable to touch uron other points in which I find myself totally disagreeing with Prof. Wiliam on. I cannot, however refrain from expressing my astonishment at the persistence of the histological views implied by the description of the "cambium," or growing cellular tissues of plants, as "some protoplasmic ele-lowing:ment," or again as "some protoplasmic layer." Similar expressions were used by Nehemiah Grew about 200 years ago, and employed for some time by writers subsequent to him. the present I imagined their interest was wholly historical. W. T. THISELTON DYER

At

THE points at issue between Prof. Williamson and myself remain in the same position as at first. He has not yet answered one of my objections. He still holds that in Lepidodendron we have a vascular medulla, outside which is a series of fibro. vascular bundles which are not closed, but go on forming new tissues by means of a cambium layer like a dicotyledonous stem. From my own observations, and from the study of recent Continental authorities, I have no hesitation in stating that the central "medulla" of Prof. Williamson consists of the united closed fibro-vascular bundles, while the investing cylinder is the modified primitive tissue which increases in diameter by means of the meristem layer of Nägeli. If Prof. Williamson will refer to Sachs' Lehrbuch, Ed. 2, p. 397, he will find good reasons given for the statement there made, that Isoëtes contains no cambium in the stem; but that the stem increases in the same way as Dracana, i.e. by a meristem layer in the primitive tissue. As long as Prof. Williamson believes in a central vascular medulla in these Lycopodiaceous stems, all his other conclusions must likewise be false. W. R. M'NAB

Royal Agricultural College, Cirencester, Oct. 21 [*.* We would suggest that this controversy be now closed, until the publication of Prof. Williamson's new material.—ED.]

Blood-Spectrum

IN the account of the Progress of Science in Italy in NATURE for October 12, Mr. W. Mattieu Williams says that Prof. C. Campani has shown that the spectrum of an ammoniacal solution of carmine is undistinguishable from that of blood, and that perhaps I should be able to tell whether any difference can be distinguished by more minute examination. In my first paper on this subject, so long ago as 1865*, I alluded to this similarity, and in subsequent papers + I have shown how the colour. ing matter of blood can be distinguished from that of cochineal, and even a small quantity recognised when mixed with a rela tively considerable quantity of that dye. I have always argued that in such inquiries we must not rely on the spectrum, but compare the action of various reagents. On adding a little boric acid to an aqueous solution of blood, no change takes place in its spectrum, whereas that of cochineal is completely altered. This effect is not produced in the case of carmine suspended in water, but the absorption-bands of blood are at once removed by deoxidising the solution with a ferrous salt, which, on the contrary, has no effect in the case of carmine or cochineal. Weak acids decompose haemoglobin into hæmatin, which gives entirely different spectra, but they do not cause any permanent change in the colouring matter of cochineal or carmine. In my opinion there is no more probability of an experienced observer mistaking these substances for blood, because the ammoniacal solutions give nearly the same spectrum, than of a chemist confounding aluminium bronze with gold, because they are of nearly the same colour. H. C. SOK BY

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Besides the February epoch, any extended list of auroras will indicate two or three others, the most remarkable of which is that of November 13-18 (See Olmsted's paner in the Smithsonian Contributions, vol. viii.) Fifty-three brilliant auroras have been observed since 1770. Of these, an accidental distribution would a-sign but one to the interval between the 13th and 18th of November; whereas eight of the number have actually occurred at that epoch. Are such coincidences accidental, or do they warrant the conjecture that, as in the case of shooting stars, there are particular periods at which the grand displays of the phenomenon most frequently occur?"

Forms of Cloud

THE form of cloud represented by Prof. Poey in his figure a, in this week's NATURE, is very similar to that described by the Rev. C. Clouston, LL.D., in his "Explanation of the Popular Weather Prognostics of Scotland," published by A. and C. Black in 167, and also in Dr. Mitchell's paper "On the Popular Weather Prognostics of Scotland," Edin. New Phil. Journal, Oct. 1863. Dr. Clouston says that, "when properly developed it was always followed by a storm or gale within twenty-four hours. It is called 'pocky cloud' by our sailors."

He gives a sketch from which, as he says, "it will be seen that this is a series of dark, cumulus-looking clouds, like festoons of dark drapery, over a considerable portion of the sky, with the lower edge well defined, as it each festoon or pock' was filled with something heavy, and generally one series of festoons lies over another, so that the light spaces between resemble an Alpine chain of white-peaked mountains. It is essential that the lower edge be well defined, for a somewhat similar cloud, with the lower edge of the fe toons fringed, or shaded away, is sometimes seen, and followed by rain only."

Dr. Clouston concluded his notice by saying, "this cloud is well known, and much dreaded by Orkney sailors." ROBERT H. SCOTT

Meteorological Office, London, Oct. 20

Elementary Geometry

It is scarcely worth while for an anonymous writer to defend his opinions; but since a sentence in my letter of September 21 still continues to elicit remarks, I may be allowed to add an explanation of my meaning. I stated that "no child is capable of taking in a subject, especially if it involves logical thought, except by very slow degrees; and must at the beginning commit much to memory which he does not comprehend." And I called this "a fact." Mr. Wormell says in reply, that the purpose which geometry serves is not the exercise of the memory, and that it is useless if not understood. I entirely agree with him, and my words, if fairly interpreted, do not convey the contrary opinion.

In your last issue Mr. Cooley writes, that my principle, that "a child must of necessity commit much to memory which he does not comprehend," appears to him totally erroneous, and not entit ed to be called a fact. But surely the order of Nature with children is to possess themselves of empyrical knowledge by the exercise of memory, and subsequently to get to comprehend what they have thus acquired. Would Mr. Coley wait until he had made a child comprehend the principles of the decimal scale, before he taught him to add up two rows of figures, and to say, "five and seven are twelve; put down two, and carry one"? If he condescends to the usual course of a "hearer of lessons" in this one instance, he acts upon the admission of my principle.

To apply this to geometry (and perhaps I may be borne with if I use Euclid in illustration): I fancy that many a boy at the beginning understands the three first propositions, but not the whole of the fourth. My plan would be, not to keep him at it till he did, but to let him learn it fairly well by rote, and go on, applying the results of the fourth by an act of faith. The second time he went through the book, if he had been decently taught,

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