August i i, 1898] 



NATURE 



343 



Nevertheless, in spite of the really small increase of 

 our knowledge in comparison with the great difficulty of 

 the problem involved, there has been no lack of specula- 

 tions, more or less scientific, on a subject which has 

 evidently exercised a not unnatural fascination on many 

 minds. The authors of these elaborations of the original 

 theory, of whom M. Faye is perhaps the best known 

 example, have all borrowed at least the central idea of 

 Laplace, deriving the whole solar system from a single 

 aggregation by some process of successive annulation. 

 This is the course adopted by General Lafouge, who, how- 

 ever, is not content to start with a nebula endowed with 

 sensible heat and angular momentum. He imagines the 

 nebula to exist in its initial stage of an indefinite and irre- 

 gular shape at a temperature of o° on the absolute scale, 

 and in this mass the attenuated constituents, dissociated 

 by the cold, are perfectly intermixed. Such a process of 

 dissociation is not in agreement with what is known of 

 the properties of matter, and little can be said in favour 

 of the assumption. The homogeneous material of the 

 nebula is, in the author's hypothesis, subject to molecular 

 cohesion, but not to internal attracting forces. Yet the 

 nebula is under the attracting influence of external bodies 

 from which are derived motions of translation and 

 rotation, together with the formation of a central 

 nucleus of increased relative density, while the whole 

 body takes a spheroidal shape as it loses its homo- 

 geneity. The action of tides, which is here made 

 use of, though rather vaguely described, is beyond 

 all doubt an influence of the highest importance in 

 the early history of the nascent system. But to attri- 

 bute great dynamical effects to external attraction, while 

 denying the evident result of mutual attractions of the 

 several parts of the nebula itself, is, if we have correctly 

 apprehended the author, an absurd inconsistency which 

 makes us distrust the whole theory as here presented. 

 And yet, while denying that internal gravitation is oper- 

 ative, General Lafouge supposes a molecular cohesion 

 sufficient to cause the nebula to finally " tourner tout 

 d'une piece." 



A dense central nucleus is now formed, as the author 

 is careful to explain, by the attraction of exterior masses. 

 No thermal effect arises from this operation, because no 

 internal work is done ; but the nucleus acts as a centre 

 of attraction to which the outer parts are drawn. In 

 this way heat is developed, and the angular velocity is 

 increased by the contraction in volume, just as in the 

 theory of Laplace. Dilation of the nucleus takes place 

 as a consequence of the rise of temperature, and, assisted 

 by the centrifugal force, a stratum of the nucleus rises 

 until equilibrium is attained under the pressure of the 

 materials descending from the outer regions. In this 

 way a ring is formed, which is later to give birth to the 

 first planet. Meanwhile more rings are formed in the 

 same way, towards the outside of the nebula, the outside 

 ring, and consequently the outside planet, being formed 

 last, as in M. Faye's system. The nucleus, however, con- 

 tinues to be enlarged by additions from the outer material, 

 and by the dilation caused by the heat disengaged, until 

 finally it absorbs the rings to which it has given rise. 

 Under new conditions of pressure the ring splits up into 

 vortices, which gather up the scattered fragments of the 

 ring and form an agglomeration, which remains as a 

 NO. 1502, VOL. 58] 



planet, while the central mass, after absorbing all the 

 residual matter of the original nebula, finally contracts 

 as it loses heat by radiation. For the explanatory details 

 of the actual conditions of the solar system, and for a 

 theory of the origin of comets, space cannot be found 

 here, and on these points the essay itself must be 

 consulted. 



Although the sources from which General Lafouge has 

 gathered his ideas are not very frequently acknowledged, 

 there seems to be reason to suppose that many of them 

 are not original. Doubtless the plan of the author was 

 to advance a theory which should commend itself as a 

 reasoned whole, and therefore the origin of an idea 

 seemed to him of little importance compared with its 

 intrinsic merit. Thus the division of rings into multiple 

 branches by means of currents from the polar regions 

 seems suggested by an idea of M. Roche ; little or no use 

 is made of these multiple branches, however. On the sub- 

 ject of solar heat again, a view is advanced which seems 

 a mere modification, without improvement, of the dis- 

 credited theory of Sir W. Siemens. Originality and 

 sound argument have not entered in large proportion 

 into the composition of this essay, which, however, is 

 probably not much worse and certainly not much better 

 than many of its predecessors, elaborated with the same 

 object in view. New facts acquired by the use of special 

 apparatus may warrant or necessitate enlarged discussion 

 of the theory of the origin of the cosmos ; but to us it 

 appears that science is not edified by these attempts to 

 explain cosmogony by simply supplementing our very 

 meagre knowledge of the operation of natural laws by a 

 mass of conjectural hypotheses. Surely Laplace is right 

 in saying : " Ces phenom^nes et quelques autres 

 semblablement expliquds, nous autorisent h. penser que 

 tous dependent de ces loix, par des rapports plus ou 

 moins caches, qui doivent etre le principal objet de nos 

 recherches ; mais dont il est plus sage d'avouer I'ignor- 

 ance, que d'y substituer des causes imaginaires." 



OUR BOOK SHELF. 

 Photographische Bibliothek^ Nos. 9 and 10. Das Fern- 

 objektiv. By Hans Schmidt. Pp. vi 4- 120. Der 

 Gutmnidruck. By J. Gaedicke. Pp. vi -I- 79. (Berlin : 

 Gustav Schmidt, 1898.) 



In the first of these two books Herr Hans Schmidt has 

 brought together a good account of the manipulations 

 necessary for the effective and successful working of the 

 tele-photographic lens — the lens of the future, as he terms 

 it in his preface. He divides his subject into four parts, 

 the first two dealing with lenses generally, and the tele- 

 photographic lenses, namely Steinheil's, Voigtlander's, 

 and Zeiss's, in particular. In Part iii. he discusses their 

 employment for obtaining pictures of different styles, 

 such as architecture, portraits, landscapes, concluding in 

 the fourth and last part with the practical work of setting 

 up the apparatus, and the other manipulations previous to 

 obtaining the finished picture. 



Those who work with or intend to use lenses of this 

 kind, cannot do better than consult this book, which is 

 written by one who is familiar with their intricacies. 

 Numerous reproductions from negatives, taken by the 

 author himself, illustrate the several types of pictures 

 which can be successfully obtained with these lenses. 



In the second of these books the author, Herr J. 

 Gaedicke, treats of the process, a form of direct pigment 

 printing, that has proved so successful. Although the 



