172 



NATURE 



{Dec. 26, 1889 



what the author says on this point : — " Gravity is regarded 

 as .... an original property of a body belonging 

 to it of itself. Descartes denies it. Therein consists the 

 opposition between Galileo and Descartes ; with gravity 

 he was obliged to reject gravitation and the power of 

 attraction. Therein consists the subsequent opposition 

 of Newton and Descartes ; he is, therefore, compelled to 

 deny the so-called central forces, as well as every actio in 

 distansP 



The two essential pre-suppositions of his hypothesis are 

 the "immeasurableness of the universe and the nullity of 

 empty space. From the first it follows that the universe 

 is not a spherical body, and does not consist in concentric 

 spheres to which the stars are fastened ; that there is, 

 therefore, no celestial sphere beyond the farthest planet 

 (Saturn), and that the sun does not lie in the same 

 spherical superficies. From the second, it follows that 

 the spaces of the heavens are filled with fluid matter, and 

 that the heavenly bodies are surrounded by the latter, 

 and subject to its influences." 



Descartes supposes the earth to be completely sur- 

 rounded by this fluid, and " acted upon uniformly in 

 every direction, or carried along by its current, as a solid 

 body in liquid matter. The planets follow also the same 

 rule. Each is at rest in the heavens in which it is, and 

 all the change of place which we observe in those bodies 

 follows from the motion of the matter of the heavens 

 which surrounds them on all sides." 



By supposing, again, that this flow of the matter, which 

 surrounds the earth and planets, describes a current 

 "spinning round like a vortex," with the sun in the 

 centre and the earth and planets going round it ; he 

 obtains, without considering their weight and attraction, 

 a method by means of which their various motions may 

 be explained. He compares this "vortex" motion of the 

 matter with eddies of water, " as waters when they are 

 forced to a'reflux form an eddy, and draw violently within 

 their rotary motion, and carry along with them, light 

 floating bodies, as, for example, straws ; as then these 

 bodies, seized by the eddy, turn about their own centre, 

 and those nearer the centre of the eddy always complete 

 their rotation earher than the more distant ones ; as, 

 finally, this eddy always, to be sure, describes a circular 

 figure, but almost never a perfect circle, but extends itself, 

 now more in length and now in breadth, wherefore the 

 parts at the periphery are not equally distant from the 

 centre, — so one can easily see that the motion of the 

 planets is of the same character, and that no other con- 

 ditions are necessary to explain all their phenomena." 



Thus Descartes agrees with Copernicus and Galileo 

 with regard to the hehocentric motion of the earth and 

 planets, although basing his hypothesis on different 

 mechanical laws ; he also teaches that the earth is a 

 planet, and rotates on its axis daily, and revolves yearly 

 in an elliptical orbit round the sun. 



The author then tells us how Descartes, after the com- 

 pletion of his hypothesis, postponed its publication, on 

 account of the fate of Galileo, and how he (Descartes) 

 expressly stated at the end that " his hypothesis not only 

 may be, but in certain respects is, false." Although he 

 denied the movement of the earth, it was only in a sense 

 that followed from his idea of motion which he applied 

 to the heavenly bodies ; for, with reference to the other 



bodies in the heavens, it does move, but is at rest in 

 relation to the fluid matter around it, or, as the author 

 says, " it moves exactly as a man who is asleep in a ship, 

 while it takes him from Dover to Calais." 



In conclusion, we must add that the work of both 

 translator and editor has been honestly done, though, as 

 the above quotation shows, the style of the translator is 

 susceptible of improvement, and that this volume will 

 form a valuable addition to the libraries of students of 

 moral philosophy. To the readers of such a work as 

 this, consisting as it does of so many historical facts, an 

 index is imperative, and we hope in future editions to see 

 one, inserted. W. J. L. 



A TEXT-BOOK OF ORGANIC CHEMISTRY. 

 A Text-book of Organic Che7nistry. By A. Bernthsen, 

 Ph.D., formerly Professor of Chemistry in the Uni- 

 versity of Heidelberg. Translated by George McGowan, 

 Ph.D., Demonstrator in Chemistry, University College 

 of North Wales, Bangor. (London : Blackie and Son, 

 1889.) 



THIS work furnishes an excellent elementary account 

 of the principles of organic chemistry. An intro- 

 duction treating of the general theory of organic com- 

 pounds, including the subjects of constitution, isomerism, 

 physical properties, &c., is followed by the detailed de- 

 scription of the various classes of compounds and their 

 relations to one another, the fatty compounds being first 

 discussed, and then those belonging to the group of aro- 

 matic substances and to the pyridine group. The treat- 

 ment of the various compounds in " series," all the 

 hydrocarbons of the fatty series — paraffins, olefines and 

 acetylenes — being, for example, fully described before any 

 of their halogen derivatives or of the alcohols are dis- 

 cussed, cannot be commended from the point of view of 

 the novice to the science, for whom the book is avowedly 

 designed. This evil is, however, largely compensated for 

 in the present work by the clear language invariably em- 

 ployed, and more especially by the frequent introduction 

 of semi-diagrammatic tables showing the connection 

 between various related series, such, for example, as the 

 glycols, hydroxy-acids and dibasic acids. 



The description of the aromatic compounds, prefaced 

 by a short account of the benzene theory, is grouped 

 alDout the typical hydrocarbons, benzene and its deriva- 

 tives being first treated, then diphenyl with its derivatives, 

 triphenyl-methane and its group, naphthalene, &c. Mere 

 description of compounds is sternly and consistently 

 avoided, its place being supplied, [whenever possible, by 

 tabulated statements, showing at a glance both the 

 chemical and physical relations of a whole series of 

 derivatives. These tables are a distinguishing feature of 

 the book, and impart to it a clearness and conciseness 

 which will render it welcome to every student. 



Abundant references are provided to the original papers 

 concerning subjects which fall without the elementary 

 scope of the work, such as, among many others, the 

 diazo-derivatives of the fatty series, the syntheses of glu- 

 cosides, and the grouping of atoms in space, which last is 

 treated in language which will perhaps be apt to mislead, 

 and scarcely receives a degree of attention commensurate 

 with its importance. 



