the axis of the planet to its orbit. But our information concerning Mars does not stop here, for astronomers are sufficiently convinced of the existence on its surface, of continents, islands, oceans, seas, straits, and inlets, to have given them such designations as W. Herschel Continent; Kepler, Lockyer, &c., Lands; Phillips Island; Dawes Ocean; De la Rue Sea; J. Herschel Strait; Nasmyth Inlet, &c., as may be seen from Mr. Proctor's interesting chart in the work under review; and if these surmises be correct-if the fair face of Mars is divided into land and water, and if its skies are varied with clouds and sunshine, it is only a reasonable inference that in every other respect its physical aspect resembles that of our own earth; its continents being diversified by hill and dale, plain and valley; its valleys adorned with lakes, and serving as the beds of rivers; whilst waterfalls will likely adorn its hill sides, and glaciers its mountain recesses. And if so, cui bono? Are there no trees and shrubs to draw their nourishment from its streams and watercourses? no insects nor other flying things to flutter in its sunshine? no living, moving beings to wander over its vast continents? And if some of these should still be absent, has all this beauty been produced in vain for ever? We leave the common sense of our readers to dictate the answer, for they are as well able to form an opinion on the matter as the author of the work before us.

From the slight inclination of its axis, Jupiter has no seasons in the ordinary acceptation of the term, but probably the planet possesses a cloud-laden vapour with its consequences. It is possible that Jupiter may be in a condition somewhat similar to that in which our earth was when its seas swarmed with ancient forms of life. Mr. Proctor does not say so, but judging from the necessity of a supporting medium for its animal races (if it possess any), in consequence of their additional weight as compared with those on the earth's surface, as will be explained presently, and from other circumstances, such a view is worth consideration. Saturn, too, has probably an atmosphere laden with vapours; and here our knowledge, which can hardly be called positive, of the phenomena favouring the existence of life in other parts of our Solar system, terminates.

There are, on the other hand, certain well-established phenomena which render life impossible upon certain other spheres. The photosphere of the Sun consists probably of glowing vapours, amongst which those of many well-known elements, such as iron, calcium, magnesium, as well as hydrogen gas, have been distinctly traced by spectrum analysis; and so, too, similar elements in the same form, sodium, magnesium, iron, hydrogen, have been clearly ascertained to exist in some of the fixed stars. In such an atmosphere, it is

6

*See Huggins "On Recent Spectroscopic Researches," Quarterly Journal of Science,' April, 1869.

safe to say that no beings at all resembling those which live on earth could possibly exist. Again, that side of the moon which is visible to us has, in all probability, neither atmosphere nor water, and it is subjected to the unimpeded action of the sun's rays for the space of fourteen days without intermission, a protracted tropical day, which is followed by an Arctic night of equal duration. Although there are grounds for believing that in past æons our satellite may have been the abode of life, it is hardly possible, for the reasons named, that it can be so in our time.

Again, there are circumstances from which it may reasonably be inferred that even where it is legitimate to assume the existence of living creatures on certain orbs, they must be constituted differently from those we know on our globe. For example, an object which on the earth's surface weighs 1 lb., weighs only 7 oz. on Mercury, but the same object would weigh 2 lbs. on Jupiter; so that a man of 10 stone here would have to carry 25 stone on Jupiter, and only 4 st. 6 lbs. on Mercury; and Mr. Proctor, if he had wished to indulge his lively imagination more freely than he has done, might have conceived of Mercury as an advanced planet, peopled by a superior race of beings, who having a lighter weight to carry and consequently less need for muscular exertion, would probably require only one meal a day to compensate for physical waste, and would therefore have more time and energy to devote to higher occupations than mere nutrition. And, as already mentioned, the additional weight which creatures would have to carry on Jupiter, with its present size and density, suggests the idea of its containing vast seas, that support Ichthyosaurs and their congeners. These are, of course, speculations, like Mr. Proctor's; but it may be as well to mention that on all matters involving biological as well as physical considerations, even speculators should be conversant with the past history of life on our earth; should be geologists and palæontologists as well as physical and astronomical observers. The more we study Nature as a whole, the greater the need appears for a school of thought which shall embrace all natural sciences.

In regard to the condition and habitability of other spheres, one consideration-for it is absurd in the present state of our knowledge to talk of conclusions-seems to press itself upon us, namely, whether smaller orbs, as the nearer planets (Mercury, Venus, the Earth, Mars), and the satellites in the Solar system, do not mean advanced life, or (as on our Moon) life already passed away; and the larger planets, and the Sun itself, retarded inorganic and organic existence.

Those who desire to be fully informed as to Mr. Proctor's views on these matters must turn to his interesting pages; but it may be remarked here, that he believes the exterior planets to be what may be called semi-solar in their character, not only receiving heat from

the Sun, but, from their peculiar condition, having the power to impart more than they receive, and so serving as suns to their systems of satellites which he regards as true worlds. Why under these circumstances he talks of Uranus and Neptune, which he includes in his subsidiary Solar system,-indeed he speaks of Jupiter, Saturn, Uranus, and Neptune as "four suns "*-as Arctic planets it is difficult to understand.

Having dealt with what may be termed the legitimate portion of his subject-the habitability of the spheres-in the first half of his book, the author proceeds to consider such objects and phenomena as meteors and comets, the other suns, nebulæ, and he concludes his volume with a chapter on "Supervision and Controul."

We have space only for two or three passing criticisms. Mr. Proctor adopts and enlarges upon the meteoric theory of the universe, which differs from the nebular theory of Laplace, in assuming that at some time or other there was a chaos of moving meteors and that these agglomerated into masses. In our Solar system, for example, the sun first drained space of an immense quantity of meteoric matter, leaving but little in its own immediate neighbourhood, so that first smaller planets were formed; but as the attractive force of the central orb diminished, larger centres (Jupiter, Saturn, &c.) were again set up; whilst in other portions of the universe similar processes were going on. This hypothesis has received, and will continue to receive, much attention. It is a kind of Darwinian theory of the universe, not attempting to go back to the beginning (for it is as difficult to account for the formation of a meteor as of a sun), but endeavouring to reason by strict logical induction from known and present phenomena to the probable past. Whoever reads Mr. Proctor's argument, however, will be struck by his straining to appropriate all known phenomena, even such as offer contradictory evidence, in his own favour; whereas, many of his facts or supposed facts are quite as applicable to the views of Laplace as to the Meteoric hypothesis; and such phenomena as the gaseous nebulæ, their proximity to star systems, and their probable absorption by such systems, tell at least as strongly against, as for, the theory which he has adopted. Here, too, in his great flights of fancy the author fails to see the full significance of some of the phenomena to which he refers. Astronomers are in the habit of saying that we see creative processes now going on in the heavens; meaning thereby that we see nebulous matter being formed into worlds today. In all probability this is only true in one sense. The author, quoting an anonymous writer, shows that we see many of the distant stars, not as they are to-day, but as they were in ages past, for their distance from us is so enormous, that the light which brings us

* P. 174.

intelligence of their condition has been ages in speeding through space. The application of this fact to the appearance of nebulæ and what may be considered as worlds in course of formation, is not dwelt upon sufficiently; for just as we see the formed suns as they existed in past æons, so do we now observe the condition of nebulous masses as they formerly existed. Here, again, a little paleontology and archæology would have done the author no harm. Just as the Almighty has left us fossils in our terrestrial strata, flints in our burial mounds, and inscriptions upon our tombs to instruct us in the past history of the earth and its inhabitants, so He unfolds to us-not as with His all-seeing and omniscient faculties, but through the very imperfection of our senses, through our inability to leave the surface of our little earth, and the consequent necessity that we should stay here and await the intelligence of the past,-so, we say, he shows us the whole history of the universe at one glance, revealing to us to-day stages of formation and progress which existed at periods long past, in a ratio of time measurable by the space through which the message-bearing ray has had to pass in its mission of knowledge. In other words, as soon as our instruments enable us to measure the distance from us of a fixed star or nebula, and show us its condition, we are able to compute at what period of the past, reckoning backwards from to-day, the object we are viewing was actually in that condition, and we have therefore a more precise method of ascertaining the time which has been requisite to bring about cosmical changes than we at present possess for determining the periods required for the deposition of terrestrial

strata.

As to Mr. Proctor's views on "Supervision and Controul," they are as suggestive as all his other chapters, but they are not likely to gain much favour, from the author's timidity in expressing his views on controverted subjects. It is not difficult to guess what these are; but when a writer says he will give us an insight into the nature and operations of the Almighty, but he sees no advantage in making people uncomfortable by saying what he himself thinks on just those matters on which he is best able to form a judgment, his views of Divine action are not likely to be much heeded either by "believers" or "unbelievers." The book has other faults. It is of too mixed a character, treating in some places (as where the principles of the spectroscope are explained) of physical phenomena in terms suited for a schoolboy, and in others discussing controverted points in astronomy with the earnestness and particularity of an experienced disputant, and not always without the suspicion of some little unphilosophical animus.

No one will accuse us, after these criticisms, of having followed the too common but ignoble practice of handling tenderly, if not of flattering, the productions of a collaborateur, but we are bound to

say in conclusion, that we have been much charmed by the perusal of the work. It is in many places very poetical; its author shows himself to be a careful and earnest observer, and the novel aspects in which old phenomena are presented to the reader are deeply interesting and often startling. The beautiful chromo-lithographs are amongst the best we have seen, and they convey vivid impressions of the heavenly bodies which they are intended to represent.

COMPARATIVE LONGEVITY.*

MR. LANKESTER has published an Oxford prize essay on Longevity, and his little book merits the attention of a wider circle of readers than it would be likely to find within the precincts of the University. The title was, of course, not of the author's choosing, and as originally given out was as follows:-The Comparative Longevity of different Species of Lower Animals, and the Longevity of Man in different States of Civilization.' As the author very properly says in his preface, "The subject does not admit of very satisfactory treatment from a scientific point of view, and is accordingly one which probably few persons would have selected to write upon, unless under special circumstances," "but at the same time," he remarks, "longevity is a subject of great popularity, and hence the facts and arguments herein set forth may, it is hoped, interest the public.'

Although we should not feel justified in complimenting the author upon his treatment of the question from any other than a scientific point of view, and are unable to accredit him with success in having imparted greater popularity to this subject, we have no doubt that the essay will materially add to his rapidly increasing reputation as an accurate observer and promising naturalist, for every page bears evidence of careful thought and extensive reading.

In conformity with the apparent wishes of the examiners or judges, he has divided his subject into two sections, the first of which treats of longevity in organisms generally, and the second of longevity in man.

His definition of longevity would be apt to puzzle non-scientific readers, for it is "the length of time during which life is exhibited in an individual;" but the meaning intended to be expressed, as subsequently explained, is that it is the "potential duration of life" in an "individual," as distinguished from a group or succession of individuals, as in the case of asexually-produced polyps, for ex

*On Comparative Longevity in Man and the Lower Animals.' By E. Ray Lankester, B.A., Oxon. Macmillan & Co.