^86
��[Voi„ v.. So. 118,
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��1b only apparent in high velocities. For nearly all BtudieB, it will sullicc to consider the deHco- tions as if produced on a sphere.
Ritter'a spcculatioos concerning the gaseous condition of the earth's interior are of espe- cial importance, inasmuch as they may tend to counteract the very positive statements made by English physicists and geologists in recent years in r^ard to the age and contraction of the earth as determined by its cooling. The English school generally regards the earth as essentially solid, with a great central volume of dense matter at a high, and, roughly speak- ing, uniform temperature. On the basis of certain plausible assumptions concerning the original temperature and conductive power of the mass, it has been possible to approximate fairly well to the age for an earth of such char- acters, and to determine roughly the shorleninp of its radius, and consequent diminmion of circumference since it has had a definite solid crust on which water might condense from the vaporous atmosphere into the oceans. The age of an earth thus limited has greatly reduced the estimates in vogue by the follow- er of Hutton and Lyell, even though its years are still to be counted by millions. Us contrac- tion from cooling has also been pronounced insufficient to produce the observed structure of mountain ranges in the way that £!lie de Beaumont had suggested. Strongly contrasted with these assumptions and their legitimate results are the conclusions reached by Rittcr. His original papers were published in Poggen- dorlTs ' Annalen,' and have received an approv- ing review from so trustworthy a physicist as Zoppritz. Giinther quotes largely from the latter. We cannot here do justice to the hy- pothesis, for it would need a somewhat delib- erate statement to make it clear. Excessively dense vapoi's, probably dissociated from their ordinary combinations, and existing at tem- peratures high above their ' critical point,' are aupiwsed to occupy the earth's centre ; and from these there is a gradual transition to the solid superficial crust. The cooling of such a central mass follows a paradoxical law, — the more heat it loses, the hotter it becomes, — and BO the supply of interior heat is long main- tained, and the time allowed for geological processes is lengthened. Moreover, the con- tractional theory here finds a cause for all the diminution of interior volume demanded by the wrinkling of the crust in mountain ranges. Altogether, while the venturesome hypothesis is very far indeed from any thing like dem- onstration, its consideration is profitable if it prevent our settling down prem.iturely to a
���Used I>elief concerning the condition of the earth's interior.
We shall wait impatiently for the second volume of the work, in which the physics of the air and sea will be discussed ; and it will be particularly interesting to see what treatment so learned an author gives to the physical geography of the land.
��Ai.i. who are interested in the pliysiology of the nervous system in lower animals will find in this volume ri most useful popular contribu- tion to this subject. The book, as the author states, is restricted to experiments made in his own researches; but these are so numer- ous and varied that it will be found to contain a summary of the most important results in this line of investigation which are at pres- ent known.
•Do they feel?' and "Have thej- senses?' are questions which are very naturally asked by any one who watches the varied movements of the jelly-fishes, star-fishes, and sea-urchins. A natural cre<]ulity prompts one to question whether the medusae, whose bodies contain over ninety-eight per cent of water, have a nervous system, and ot^ans of special sensa- tion. Twenty-flve years ago, science would have given a very unsatisfactory answer to these questions ; but to-day we have a very accurate knowledge of the anatomy of these structures. With this advance in anatomical knowledge, physiological research has kept pace ; and certainly no one has done more than Romanes in this kind of researeh. Thanks to these advances, we can now reply to our questioner with more confidence than Ibrmerly. These animals not only feel, but also have special organs of sight, hearing, and probably smell.
The author puts the anti-viviseclionists in « receptive frame of mind for the work which follows by declnriug, in the introduction, that his e.tperiments on living animals involve no pain, and that the " consciousness which is present must be of a commensurately dim and unsuiTeringkind."
The work is mainly taken up by experi- ments in excising portions of the body, and noting the effects on the movements of the animal. Many very interesting experiments
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