Графични страници
PDF файл
ePub

A

Where the depth was great, however, and especially when the surface drift was considerable, special precautions had to be observed, the chief of which was to move the vessel by steam up to windward, so as to counteract the leeway. An additional device was to attach a weight (1 or 2 cwt.) to the dredge rope at some distance from the dredge-usually about one-fourth of the known depth. The annexed figure (for which, as for the other intercalated cuts, the editor is indebted to the Secretary of the Royal Society) gives an idea of the relative positions of the vessel and the dredge according to this plan of dredging.

[merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small]
[blocks in formation]

A represents the position of the vessel when the dredge is let go; A B the line of descent of the dredge. While the dredge is going down, the vessel drifts to leeward, say to c, when c WD would represent the relative positions of the vessel, the weight, and the dredge itself. E, F, G, H, are the positions of the vessel in steaming to windward, during which time the dredge sinks from D to B, and the weight from w to w'. This operation is repeated two or three times, and the vessel is then

[blocks in formation]

allowed to drift, and to carry forward the weight w1, so that the dredging is carried on from the weight, and not directly from the vessel. In this way the dredge is quietly pulled along, its lip scraping the bottom in the attitude which it assumes from the position of the centre of gravity of its iron frame and arms, and a much smaller quantity of rope is required in proportion to the depth than in ordinary in-shore dredging. For the 2,435 fathoms' dredging, 3,000 fathoms of rope were employed, and during the time when the writer was on board, 2,000 fathoms of rope were used for depths ranging from 1,200 to 1,476 fathoms.

It is with great satisfaction that we have heard that her Majesty's Government have granted the use of the Porcupine and her apparatus for a cruise in the Bay of Biscay and the Mediterranean during this summer, under the same scientific charge as before, and that her talented and experienced captain will be still in command of her. The scientific public will await the results of this expedition with great interest.

EXPLANATION OF PLATE.

The plate represents the quarter-deck of the Porcupine in Galway Dock, June 1869 (from a photograph).

291

REVIEWS.

IT

OTHER WORLDS THAN OURS.*

T seems as if each department of science had its own especial epoch or period, when, by reason of its popularity, or the importance of the discoveries revealed by those who belong to it, it becomes more prominent than usual. Just in such an epoch does astronomy appear to be at the present time. The great improvements in telescopic construction, the comparative cheapness of instruments with which original research can be conducted, the wonderful applications of spectroscopy and photography to astronomical enquiries, all have helped to render the study of the heavens, not only a pursuit open to thousands who hitherto never looked at a star, but have also by the revelation of some of the most wonderful phenomena in nature, given astronomy an importance which it hardly had before.

The time, therefore, had come when a treatise embodying the results of later researches, and giving, as it were, a bird's-eye view of our knowledge of the celestial bodies, as it now exists, was required; and such a treatise Messrs. Longmans have given us in the excellent volume now under notice. Mr. Proctor-who is at once a teacher, an investigator, and a writer-combines the three qualities essential to the construction of such a work as that to which we have alluded, and he has brought these into full and successful operation in his account of the modern heavens, if we may use the expression. His book is not a treatise on astronomy; it is more a work which, in the fashion of Herschel's Lectures on Scientific Subjects, deals fully, and yet with remarkable clearness, with a number of scientific problems, and which is addressed to the man of general education, whether he be an astronomer or not. But as the author treats of nearly all the astronomical questions which come within the range of the ordinary text-book, the person who carefully reads Other Worlds than Ours will learn nearly all that the scientific star-gazer has got to tell.

When we tell our readers that Mr. Proctor has chapters on the Earth, the Sun, the inferior planets, on Mars, Jupiter, Saturn, Uranus, the Moon, meteors, and comets, the stars, and the nebulæ, they will excuse our at

"Other Worlds than Ours: the Plurality of Worlds, studied under the light of recent scientific researches." By Richard A. Proctor, B.A., F.R.A.S. London: Longmans, 1870.

tempting a general analysis of the work. We may, however, dwell on some of its more novel and interesting features. These, it appears to us, are to be found in the chapter entitled, "What we learn from the Sun." In this section of his work, which is essentially controversial, the author enters upon a discussion of the several moot points in connection with the late solar observations. In reference to the sun's corona and the zodiacal light, subjects which readers will be aware have of late received considerable attention, Mr. Proctor has much to say. He enters with considerable minuteness into the consideration of Mr. Lockyer's hypothesis on the origin of the sun's corona, and he adduces certain very formidable arguments against these views and in favour of his own opinions. It would be impossible to put the author's observations into a smaller compass than he has himself compressed them, and as they occupy several pages we could not possibly reproduce them in full. We, however, may just quote one passage, which, to a certain extent, contains the pith of Mr. Proctor's ideas on the point in question. After commenting on the spectroscopic evidence as to the corona and on the "atmospheric glare" theory of Mr. Lockyer, he goes on to say :—

"Now, remembering that we have two established facts for our guidance -(1) the fact that the corona cannot be a solar atmosphere, and (2) the fact that it must be a solar appendage-I think a way may be found towards a satisfactory explanation. Let it be premised that the bright lines of the coronal spectrum correspond in position to those seen in the spectrum of the Aurora, and that the same lines are seen in the spectrum of the zodiacal light, and in that of the phosphorescent light occasionally seen over the heavens at night. Since we have every reason to believe that the light of the aurora is due to electrical discharges taking place in the upper regions of the air, we are invited to the belief that the coronal light may be due to similar discharges taking place between the particles (of whatever nature) constituting the corona. Now, though the appearance of an aurora is due to some special terrestrial action (however excited), yet the material substances between which the discharges take place must be assumed to be at all times present in the upper regions of air. In all probability they are the particles of those meteors which the earth is continually encountering. And since we know that meteor-systems must be aggregated in far greater numbers near the sun than near the earth, we may regard the coronal light as due to electrical discharges excited by the sun's action, and taking place between the members of such systems. Besides this light, however, there must necessarily be a large proportion of light reflected from these meteoric bodies. In this way the peculiar character of the coronal spectrum may be readily accounted for. We know from the auroral spectrum that the principal bright lines due to the electrical discharges would be precisely where we see bright lines in the coronal spectrum. But besides these there would be fainter bright lines corresponding to the various elements which exist in the meteoric masses. These elements we know are the same as those in the substance of the sun. Thus the bright lines would correspond in position with the dark lines of the solar spectrum. Hence, as light reflected by the meteors would give the ordinary solar spectrum, there would result from the combination a continuous spectrum on which the bright lines first mentioned would be seen, as during the American eclipse."

Such is Mr. Proctor's ingenious theory. In the present condition of astronomical science it is impossible to pronounce definitely in its favour; but it certainly fascinates us by its simplicity, and by the fact that it collates a number of otherwise heterogeneous facts; whilst it is certainly less of the haphazard and "dernier ressort" character than Mr. Lockyer's "glare" notion. At all events, whatever be its merits, or that of any of the other original ideas with which the book abounds, it is clear that Mr. Proctor's volume is a most attractive and instructive one, and one which should be carefully read by all intelligent persons who come under Mr. (now Dr.) Matthew Arnold's category.

IT

PTERODACTYLES.*

T is not many years ago that the remarkable fossils of the Cambridge Greensand which Mr. Seeley has now so well described were a veritable terra incognita to the paleontologist. Till the publication of the present excellent volume, it would have been difficult for the worker to obtain in any one treatise all the information he might have desired as to the affinities and the remains of the Cambridge Pterodactyles. But now, thanks to the author's labours, we have in this treatise an elaborate account of all that relates to the paleontological history of the Cambridge Greensand Ornithosauria. Mr. Seeley has gone elaborately into his subject, so that indeed his book may well be regarded as a handy monograph on pterodactyles generally. In his earlier chapters he gives a sketch of the organisation of these curious reptiles, and an account of the fossil remains on which the earlier descriptions of the group were founded. Next he states in outline the views taken of these affinities by Cuvier, Sömmerring, Oken, Wagler, Goldfuss, Wagner, Quenstedt, Burmeister, and Von Meyer. Then, without basing his own opinion on those which have been enunciated by previous writers, he proceeds to reason on the à priori method, and adopts the view that the pterodactyles were neither birds nor reptiles, but were a group between the two, and entitled to a place of equal rank with the class birds. The following epitome, nearly in the author's words, gives a notion of his doctrine :

"The Pterodactyles have a nervous system of the bird type; they have a kind of brain which exists only in association with a four-celled heart and hot blood; they have a respiratory organisation which only exists among birds; with that respiratory apparatus is always associated a four-celled heart and hot blood, which it would necessarily produce; and with that respiratory organisation is always associated a brain of the type that the Pterodactyle is found to possess. Therefore," says Mr. Seeley, "it is firmly indicated that the general plan of the most vital and important of the soft structures was similar to that of living birds." He then goes on to say that these avian

"Ornithosauria: an elementary study of the bones of Pterodactyles made from fossil remains found in the Cambridge Upper Greensand." By Harry Govier Seeley, of St. John's College, Cambridge. London: Bell & Daldy, 1870.

« ПредишнаНапред »