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SCIENTIFIC SUMMARY.

ASTRONOMY.

THE Eclipse of December 12, 1871.-This eclipse will probably be well observed. We have already spoken of the track of the moon's shadow, but when our last Summary appeared it was not considered likely that an expedition would be sent out from England to take any part in the work of observation. Application has been made, however, to Government, and the sum of 2,0007. has been granted, as well as transport and the means of camping, &c., for an English expedition to Ceylon. As a strong observing party will proceed from Sydney and Melbourne to the stations in northern Australia, while the Dutch Government will probably garrison suitable observing stations in Java, there is abundant reason for believing that the eclipse will be well observed. Observations in India will probably be superintended by Mr. Posson (the Government astronomer at Madras), Colonel Tennant, and Lieutenant Herschel. It is hoped that Mr. Lockyer will be able to head the expedition to Ceylon. At the present time it is, indeed, understood that he will do so, in accordance with the request of the Astronomical Society (who have felt it incumbent upon them, we understand), to urge that one or other of our principal solar spectroscopists should take charge of the English expedition; but we can regard nothing as definitely settled at this moment. It is hoped that M. Janssen may be able to go to Java. We remind our readers that in North Australia the totality will last 4 m. 18 sec., or 2 m. longer than at the best stations last December. In Java the duration will be less, and further west in Ceylon the duration will be only a few seconds longer than in last year's eclipse. A slight mistake has been made on this point, however. Mr. Hind, in his first and comparatively rough account of the eclipse, had marked the shadow track as barely extending to Trincomalee. He now so places Trincomalee, with reference to the track of shadow, that he estimates the duration of totality there at 2 m. 30 sec.; and it has been inferred that, since this is the case with a town on the border of the shadow track, places in Ceylon near the middle of the track will have longer totality. But, as a matter of fact, Trincomalee is now shown to lie very near to the middle of the shadow's path. However, there can be no doubt that, with suitable observing weather, stations in Ceylon will have a considerable advantage over the best stations for observing last year's eclipse.

As to the observations which are to be made or which require to be made, we have a few remarks to make. Photography is to be applied again,

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but under conditions which promise better success than has hitherto been obtained. In particular, advantage is to be taken of the experience acquired by Mr. Brothers last year. Mr. Brothers, it may be remembered, adopted a new method of photographing the corona, making use of an ordinary photographic lens of long focus instead of a telescope. Notwithstanding very unfavourable weather, the eclipsed sun having been clouded over until within a few seconds of the end of totality, Mr. Brothers succeeded, as we know, in picturing the corona as it was never seen on glass before." It is not to be wondered at, therefore, that it has been decided to employ the same method on the present occasion. The proposed spectroscopic observations are also promising. Two excellent 6-inch refractors are to be mounted on the same equatorial stand, one at each end of the declination axis; so that, while one observer studies the aspect of a portion of the corona through one telescope, another may study the spectrum of the same portion through the other. This contrivance has been suggested by Dr. Huggins, and appears well calculated to remove the doubts which have hitherto rested on the subject of those spectroscopic observations which have been guided merely by means of the ordinary finder. Mr. Lockyer has made suggestions, among which the following may be noticed. "At each place," he says (ie. India, Ceylon, and Australia), "the spectroscopes should be employed for half-anhour (to be on the safe side) before totality, in scrutinising the crescent at its narrowest place, and the chromatosphere outside the following limb of the moon. At each place, as before defined, there should be a spectroscope with a finder and equatorial motion (or some 'equivalent arrangement) directed to the sun's centre, to record any changes which take place in the spectrum from, say, half-an-hour before to half-an-hour after totality, and also during totality, bien entendu. The relative darkness or brightness of the lines should be recorded every ten seconds. The spectroscope should have moderate dispersion, large object-glasses for collimator and telescope, and with focal length such that two or three degrees round the sun should be take in (i.e. 1° or 14° from the sun's centre), and a large field.”. . .

Coming to the details of the expedition to Ceylon, Mr. Lockyer expresses the opinion that it need not exceed the following numbers:—

Or 8 in all.

1 telescope-spectroscopic observer; 2 assistants.

1 photographer; 2 assistants.

1 spectroscopic observer; 1 assistant.

To one suggestion of Mr. Lockyer's we are compelled to take grave exception. He notes, among observations which he regards as comparatively unimportant, "sketching anything but the changes in the corona." It appears to us, on the contrary, that the changes in the corona are precisely the phenomena which are, in the first place, most difficult to delineate; and, in

Mr. Lockyer remarks that, in his opinion, this duty may perhaps be entrusted to skilled sappers. But the history of all the recent eclipses shows that, of all the departments, the photographic is the one which requires to be entrusted to the most skilful hands. Very useful spectroscopic work has been done with very little preceding practice; but no good photographic work has yet been done save by experts.

the second, the least likely to prove instructive. We know as a matter of fact that, during the totality, and more especially at the beginning and end of totality, a variety of strangely changeful phenomena, resulting from the varying illumination of our atmosphere by the prominences, sierra, and the really solar portion of the corona, may always be noted. It would be a problem of extreme difficulty to determine the precise way in which these variations are caused; but there can be very little question that they are chiefly due to the varying amount of illumination just referred to, and to the rapid changes of temperature resulting from the passage of the moon-shadow athwart the upper regions of the air. To pay special attention to such changes is a course admirably calculated, perhaps, to throw light on meteorological questions; but it does not seem to promise any new information respecting the real solar corona. The most valuable information respecting this remarkable appendage of our sun would unquestionably be gained if one observer, not suffering his attention to be distracted by the wonderful spectacle produced by the changing illuminations of the upper air, could discriminate between the changeful phenomena of the eclipse and those features of the corona whose fixity pronounces them to be true solar phenomena.

Detection of the Annual Parallax of a Planetary Nebula.—Mr. Gill, of Aberdeen, well known as a careful observer, and as having executed some successful photographs of the moon, announced at the recent meeting of the British Association that he had detected a parallax of nearly two seconds in the case of the planetary nebula 37 H. iv., close by the pole of the ecliptic. He is desirous, however, of continuing his observations for yet another year before definitively announcing that the nebula has this large parallax. Should this result be confirmed, it would follow that this nebula is nearer to us than any of the fixed stars, or at least than any fixed star whose parallax has hitherto been measured. The result would be interesting, as confirming those doubts which have recently been expressed respecting the vast distances at which nebula have been long supposed to lie. It must not be forgotten, however, that Sir William Herschel, by whose observations these vast distances have been supposed to be established, was himself the first to express doubts on the subject. The planetary nebulæ, in particular, were among the objects which he judged, during the latter part of his career as an observer, to be much nearer than he had imagined when he enunciated his earlier but better-known theories. It is somewhat singular that the particular nebula which has thus been the first to reward the search for nebular parallax, was the first nebula which Dr. Huggins found to be gaseous. A somewhat remarkable comment is reported to have been made by Professor Tait upon Mr. Gill's paper. That eminent mathematician remarked, according to the report, that Mr. Gill's observation, if established, would tend to overthrow the theory now universally accepted among astronomers respecting nebula,—to wit, "that nebulæ are the moving matter of stars; showers of stones, Sir W. Thomson would call them, at inconceivably vast distances." We had never heard that this theory had even been enunciated among astronomers, though we have had through our hands the proceedings of all the principal astronomical societies of Europe and America, and all the most important treatises on astronomy which have been pub

lished during the last ten years. Surely, either Professor Tait or the reporters must have made some mistake.

Further Observations of n Argus and the Surrounding Nebula. Mr. Abbott submitted, two years ago, pictures of this interesting nebula to the Royal Astronomical Society, which seemed to show that the nebula had undergone important changes. He now sends a third picture, accompanied by comments on the criticisms to which his former paper was exposed. His first attack falls on Mr. Proctor, who, in an article in "Fraser's Magazine for December 1868 (presenting Mr. Abbott's work in a very favourable light), had ventured to express doubts whether the stars in Mr. Abbott's drawing of 1868 had been actually copied from the view given by the telescope, &c. Mr. Abbott says that all his drawings were carefully copied from the object as described in the 'Astronomical Register' for January 1869;" and he adds that "there is little doubt but that Mr. Proctor's views on the subject would be very much enlarged, if he had the opportunity of seeing the star and nebula as they appear at Hobart Town." Commenting on Mr. Abbott's letter, Sir John Herschel, who had been the first to express doubts as to the placing of the stars in Mr. Abbott's drawings, remarked that there was not one among all the stars delineated which he could identify with any of those laid down in his own drawings and catalogued positions. "The most superficial inspection suffices to show that there is no correspondence between us; and that Mr. Abbott's field of view of 1° 8' in diameter differs as completely from a similar field in my monograph, having 7 Argûs near the centre, as if the telescope had been directed to quite a different part of the heavens. . . . This would, however, be of little moment, were it permitted to suppose that attention had been given only to the delineation of the nebula, and that the stars had been put down at random, or with little regard to their real configurations. Mr. Abbott, however, in the paper which accompanies his diagram, distinctly repudiates this supposition, and insists on the correctness of his representations of the stars in the field of view delineated; not, indeed, as micrometrically accurate, but as careful eye-drafts." Mr. Abbott having been communicated with as to the doubts thus renewed, replies, under date February 7, 1871, endeavouring to re-establish the accuracy of his draughtsmanship. Finally, the whole series of papers has been submitted to the searching scrutiny of the Astronomer Royal, who conceded the main points, namely, that the nebula has shifted its position, and that Mr. Abbott was the first to announce this interesting fact, yet comments, in somewhat severe terms, on Mr. Abbott's drawings. "When we look closely to fundamental points," says Professor Airy, "all is confusion. Mr. Abbott's observations were all made with a refracting telescope, so that the order of the four cardinal points on the map would be EW (turned round in in any degree). But in the 1870 map he has them marked WE; in the N N 1871 map he has marked only The S'

S in the two maps differ about 45°. In each of these maps is a line (different for the two) which he calls 'Line of Light.' What this means I have not the slightest idea. In points of geometry, therefore, Mr. Abbott is a most inaccurate man. As

regards the delineation of the nebula, I cannot make out anything. It is impossible for us to publish maps in this state." We have spoken of Professor Airy's examination of the subject as final; but as a matter of fact, a letter from Captain Herschel reopens the very question on which the Astronomer Royal had expressed himself satisfied. "Mr. Abbott appears to have got wrong," says Captain Herschel, "in his N. and S. points. Is it rash to suspect that he has also mistaken ŋ? Neither does he appear to have even recognised the lemniscate. He speaks of 'a dispersion of the stars'; but his own drawing, as I now show, places most of his stars in approximately their right relative places. Surely all this betokens non-recognition, on his part, of the object he was examining, due probably to an inferior magnifying power. If his chart of the stars is as correct as I think, every atom of evidence of change in the nebula which he adduces is swept away."

η

To quote the remark with which Professor Airy opens his paper, "The subject is a very puzzling one."

Proposal for a Series of Surveys of the Star Depths.—Mr. Proctor, in a communication to the Royal Astronomical Society, indicates the necessity of a series of systematic surveys of the heavens, on a principle quite different from that on which the Herschels gauged the star depths. A series of telescopes of gradually increasing aperture should be employed to gauge every portion of the celestial sphere, the series of gauges for the several apertures being then charted isographically. His opinion of the value of such surveys is founded on the interesting results which are established by the isographic charting of all Argelander's series of 40 full-sheet charts, showing the places of 324,198 stars. It would not be necessary, however, to mark in every star separately, with careful reference to position and size, as in the isographic copy of Argelander's charts; all that would be necessary would be to mark in the observed number of stars (as determined by the gauges) in the corresponding spaces in the chart. The gauge fields should not be circular, but square (except close by the poles), so as to leave no ungauged spaces, and to avoid overlaps. By taking apertures of 3, 4, 5, 6, 8, 12, and 18 inches, or even to 2 ft. and 4 ft., a progressive series of charts would be obtained, which would throw great light on the laws of stellar distribution.

The Physical Changes of Jupiter.-Mr. Ranyard has contributed an interesting paper on this subject to the "Monthly Notices" of the Astronomical Society. He shows that, within two years of the great sun-spot maximum of 1848, the white spots on the southern belt were strongly marked, and the equatorial region much broken up. Within a year of the next sun-spot minimum, Mr. De la Rue made his large and well-known drawing of Jupiter with a 13-inch silver speculum. "It is full of the smallest details in the belts, yet there are no traces to be found of Dawes' markings, bright points, northern or southern eggs (sic), or equatorial port-holes." (We take some exception to these terms, as thus used absolutely; though they are very suitable expressions for comparative description.) Drawings made by Piazzi Smyth in 1856 entirely endorse Mr. De la Rue. But in 1858, when the sun was again marked with spots, Lassell noticed a numerous group of white spots in the bright equatorial region of Jupiter. "For several years," says Mr. Lassell, "I failed to see any such spots upon the face of Jupiter at all, but last year they appeared again in the same quarter of the