The Fairfield Orchids cultivated by Messrs. James Burke & Co. Bradbury & Evans, 1872. This is, of course, a publication got up for the purpose of selling the orchids of this firm. We believe that Mr. Leo Grindon had a share in its production.

The Stone-Age in New Jersey. By Charles C. Abbott, M.D. Salem, U.S., 1872. This is unquestionably the best paper and most elaborately illustrated which has appeared on flint weapons in any part of the world. It is admirably done, and we are glad it has been reprinted from the "American Naturalist," in which it originally appeared in last March or April.

Optical Illusions Explained. By A. B. Lacy, 1871. Is simply an explanation which exists in every treatise on natural philosophy in existence.

The Testimony of the Rocks, &c. By T. Callard. London: Elliot Stock, 1872. The whole matter is explained in about twenty-five pages of the smallest duodecimo. The author has been fortunate, we must say.

The Existence of Projectile Forces in Nature. By John Parker. New York: Wiley, 1872. The author simplifies the whole of astronomical questions, in twelve pages 8vo. !!

The Hygiene of Air and Water. By W. Proctor, M.D., F.C.S. London: Hardwicke, 1872. This is a sensible little book on two important points in Hygiene. We recommend it to our readers' notice.

Human Progress in Medical Education. By W. Aitken, M.D., Professor of Pathology in the Army Medical School. London: Griffin & Co., 1872. This is a very capital address, given by the Professor of Pathology at Netley. It will repay attention. Dr. Aitken seldom speaks without saying something to the point.

303

SCIENTIFIC SUMMARY.

ASTRONOMY.

PROPOSAL for new National Observatories.-Col. Strange has called the attention of the Royal Astronomical Society to the insufficiency of existing national observatories, in respect of what may be called the physics of astronomy. He proposes that Government should be applied to for money to found other observatories than those at present in existence, and that in these new observatories the study of the physical features of the sun and moon, planets, comets, nebulæ, and stars, should be prosecuted systematically. At present the feeling in scientific circles is in favour rather of an extension of the work done at existing observatories, than of the foundation of new observing stations.

The Eclipse of December last.—In the last number of this journal will be found the chief particulars of the observations made upon the recent eclipse. It was hoped, however, that at the March meeting of the Astronomical Society full reports would have been made by the English observing expedition, and that many details of interest would then be announced. To the astonishment, and indeed to the disgust, of the crowded meeting which assembled on the strength of this expectation, no report whatever was then made! Nor was any report delivered at the April or May meetings! The silence of those whose duty it was to report the proceedings of the English expedition has naturally given rise to much comment, by no means favourable to the nominal chief of the expedition; the more so that the said head of the expedition has made free use of the information handed in to him by his fellow-observers, as well in lectures as in papers published at a price. It is felt that (unless there be some explanation as yet unpublished) it is altogether unworthy of a student of science to refrain from making due announcement of discoveries effected by the aid of Government money, and by the skill of fellow-workers who have unsuspectingly entrusted the records of their work into his hands, unless when the announcement can be so made as to be repaid with so many pounds, shillings, and pence. We trust for the honour of British science that some explanation may yet be forthcoming.

In marked contrast to the action of the reputed head of the English expedition, is that of Col. Tennant. So soon as he had reached England, he laid his statement before the Royal Astronomical Society, and submitted to

examination the splendid photographs which were obtained at Dodabetta. It should be noticed in passing that the photographs, scarcely (if at all) less perfect, obtained by Mr. Davis, who at Lord Lindsay's charge accompanied the English expedition, escaped as by a miracle from the tight grip which laid hold of everything else obtained by that party, and were thus available for comparison with those of Col. Tennant. Nothing could possibly be more convincing than the evidence given by either series separately, and by the two series when taken together. The details of the corona in these photographs are very numerous, and wonderfully distinct; all of them can be recognised in all the photographs. We cannot wonder that even those who had been most opposed to the solar theory of the corona have at last given in their adhesion to it. We do not say that all of them have, for that would be expecting too much, human nature being as it is. But that any of the opponents of that theory should have adopted it, speaks volumes. Now Dr. De la Rue, who, it will be remembered, had urged arguments in favour of Oudemann's theory, which may be called the lunar theory of the corona, admitted, with a candour and frankness which did him infinite honour, that the photographs obtained last December demonstrate the solar nature of the phenomenon.

Densities of Jupiter's Satellites.—Mr. Proctor has called attention to the incorrect values of Jupiter's satellites which have found their way into our text-books of astronomy. These values have led to erroneous assumptions as to the condition of these bodies. The following table shows at once the incorrect values formerly adopted, and those which Mr. Proctor has calculated :

It will be seen that the errors are enormous, nor is there any recognisable explanation. For the density of the first satellite is given in our text-books at about a tenth of its true value, but that of the third at rather more than a fifth. One obtains something very like the text-book values, however, by supposing all the satellites equal in size to the first, and by reducing the thence estimated density to one-tenth of its value. Assuredly, supposing this to be the true explanation-or, indeed, whatever may be the true explanation-the error is a most monstrous one, to be repeated, as it has been, from one hand-book of astronomy to another. It may fairly be asked what confidence can be placed in such hand-books when blunders like these are suffered by their authors to escape detection.

Orbit of the Double-star Castor.-Mr. Wilson, M.A., of Rugby, enunciates the somewhat startling theory that the orbit of Castor is hyperbolic, "a form

• Probably because, being obtained at Lord Lindsay's expense, there was a private claim upon them. The public claim upon the observations of the members of the expedition could be ignored, it would seem; but, fortunately for science, Lord Lindsay successfully urged his claim upon his own property.

of orbit," as he truly remarks, "which has not been shown to exist in the case of any binary system." It may be remarked that Sir John Herschel, nearly forty years ago, deduced the period 253 years, while Smyth obtained a period of 240 years. In the Monthly Notices for December 1845, Mr. Hind gives elements" entirely differing from those previously computed by Herschel and Mädler," the difference being "materially owing to the great influence exerted by recent measures at Mr. Bishop's observatory by Mr. Dawes." Mr. Wilson's result involves a somewhat startling advance in the same direction. He finds that the apparent orbit is part of an hyperbola of eccentricity 2.2. "The real hyperbola may be shown by a graphical construction to have an eccentricity of 3·16, and its line of nodes nearly coincides with the axis major." "If this orbit is correct, the angle of position will decrease to the limit 188°. It is now about 238° 12, according to the observations of Mr. Seabroke and myself," he adds, " and a little less by the interpolating curve-about 237°85."

:

An Unsuspected Cause of Diffraction Phenomena in Telescopes.-Captain Noble makes the following remarks in the Monthly Notices for April :"Some little time ago, in observing Jupiter and his satellites, I remarked certain emanations which appeared to have their origin in diffraction. I was very much puzzled to imagine in what way these phenomena could arise. My 4.2-inch Ross object-glass is simply perfect; my eye-pieces were carefully cleaned, and, so far as I could see by removing them, and looking up the tube at the Moon or Jupiter, the tube itself was free from any obstruction. Since, however, the general definition of the instrument was sensibly unimpaired, I took no further action in the matter, and let things take their course until about the middle of last month. I was observing the sun one morning at that period, when I removed the eye-piece for some reason, and happened to glance obliquely up the tube. To my astonishment I saw, brilliantly illuminated by the sun, a perfect grating of excessively fine spider-webs, spun vertically across the interior of the telescope, somewhat within the focus of the object-glass. A light, in more senses than one, suddenly broke in upon me, and I very speedily removed the offending lines. I had the pleasure, that same evening, of viewing the Jovian system shorn of all optical appendages. I am too ignorant of the Arachnida to be able to guess at the species which produces a web of such extraordinary tenuity; but it certainly must be an extremely minute one, not only on account of the excessive fineness of the filaments which it spins, but also in order that it should have found its way inside of a tube so thoroughly and carefully closed as (I should think) to prevent the existence of interstice or aperture whatever whereby an entry might be effected."

Spectrum of the Zodiacal Light.-In our last Summary we mentioned that Liais had found the spectrum of the zodiacal light to be a faint continuous one. Before that statement had appeared in these pages, news was received from the skilful Italian spectroscopist Respighi, to the effect that the spectrum of the zodiacal light consists in the main of the bright line forming the chief constituent of the spectrum of ordinary green aurora. "Formerly," he says, "I made spectroscopic observations on the zodiacal light, in the East Indies, but I could not see Angström's line, and I had obtained no result because I did not take the necessary precautions, protectVOL. XI.--NO. XLIV.

X

ing the eye from external light whose brightness was sufficient to veil the line and the bright neighbouring zone." But his observations on the night following the great auroral display of February 4, serve, so far as they go, to prove the very reverse of what Respighi infers. He says: "Thinking that the aurora-borealis would re-appear on the next evening after the disappearance of twilight, I set myself to observe the sky, and I found it illuminated in all parts by a feeble light which produced the effect of a general phosphorescence. While waiting for marked phenomena, I directed the spectroscope provisionally towards the zodiacal light, then tolerably bright, and soon I could distinguish the green light and the neighbouring zone of light apparently continuous, and which embraced the space occupied by the lines of the auroral spectrum. Next turning the spectroscope on the faint light which illuminated the heavens, first towards the magnetic meridian, and then towards all azimuths and at all heights, I was surprised to find still the same spectrum, more or less marked, but everywhere as distinct as in the zodiacal light. Moreover Dr. D. Legge, one of the assistants at the observatory, distinctly saw this spectrum in all parts of the heavens. These observations were made towards seven or eight o'clock. Later, towards ten, I could not detect this spectrum in any part of the heavens. This fact, which confirms a similar observation made by Angström in March 1867, seems to me somewhat important, for it would tend to show the identity of the light of the aurora-borealis and the zodiacal light, and hence the probable identity of their origin." It seems to us, on the contrary, that Respighi's observation tends to show that the appearance of the auroral line when the spectroscope was turned upon the zodiacal light was due to auroral light in that direction, and not to the zodiacal light at all. It certainly was a suspicious circumstance that a certain bright line could be seen as distinctly in all parts of the sky as towards the zodiacal light; and one cannot understand why, under the circumstances, Respighi should judge this line to belong to the zodiacal light, since unquestionably any auroral phosphorescence must have extended over the zodiacal region as well as over the rest of the heavens.

But all doubts on the subject seem to be finally removed by Professor Piozzi Smyth's recent observations in Sicily. In the first place, it should be noticed that Prof. Smyth attended much more carefully to the structure of his instrument than any of his predecessors in zodiacal observation. He was also particularly careful to exclude extraneous light. He had an instrument so contrived that he could examine simultaneously the spectrum of any auroral light and the faint linear spectrum of an alcohol flame. Now with a narrow slit he obtained from the zodiacal light no spectrum at all, though the very same instrumert had, with the same slit-opening, shown the chief auroral line even from very faint aurora. As the slit was widened no trace of a linear or band spectrum could be recognised, but with sufficient opening a faint continuous spectrum, exactly like that obtained from faint twilight, or indeed from the ordinary night-sky when there is no aurora. Here we have absolutely perfect proof of the fact that the zodiacal light gives the same spectrum as faint reflected sunlight. But Prof. Smyth's observation proves more than this. It shows that, under the very same circumstances, the zodiacal light gives no spectrum where the faintest