50 



NA TURE 



[May 17, 1906 



The three closing chapters deaUng with Copernicus, 

 Tycho, and Kepler are naturally those which command 

 our special interest. They contain far more than 

 mere statements of the works of these great heroes 

 of astronomical science. They define clearly the 

 specific rdle played by each of these actors in the 

 revolution of scientific thought. In following the 

 author through his analysis of " De revolutionibus," 

 we realise not only the great mental power but also 

 the heroism of the " quiet student at the shore of the 

 Baltic," and we feel the importance of the moment 

 when his work is ushered into the world with 

 Osiander's apologetic introduction. We must agree 

 with the author's endeavour to show how little Coper- 

 nicus could have been influenced by Philolaus and the 

 vague ideas of Aristarchus, whose anticipations de- 

 tract nothing from the originality of his own thoughts. 

 On the other hand, the exposition of the defects of 

 the system is so lucid that it requires no intimate 

 technical knowledge of astronomy to recognise the 

 necessity of modification, which so immediately urged 

 Tycho to the invention of his ingenious compromise 

 between the geocentric and heliocentric conception. 



How far Tycho's all-important work as an observer 

 has paved the way for the final recognition of the 

 true system by Kepler is admirably shown in the last 

 chapter, where the author opens before us the succes- 

 sive paths along which, through a labyrinth of errors 

 and failures, the never tiring genius of Kepler was 

 finally led to the " golden portal of truth." The long 

 and weary road he had to go before he finally broke 

 away from the time-sacred idea of circular motion and 

 the Ptolemaic punctum aequans, 'and proved con- 

 clusively the elliptic character of the Martian orbit, is 

 brought before us bv an exhaustive analysis of his 

 works, the study of wiiich is so highly instructive, not 

 only from the scientific, but also from the psycho- 

 logical point of view. The reproach, often levelled 

 against the author of the " Mysterium Cosmo- 

 graphicum," of having filled his books with all sorts 

 of mystic fancies, is, in Dr. Dreyer's opinion, founded 

 on a misconception of Kepler's object in making his 

 investigations. " There is the most intimate connec- 

 tion between his speculations and his great achieve- 

 ments ; without the former we should never have had 

 the latter." 



We cannot attempt to enter upon the author's 

 review of the opinions of science and church on the 

 Copernican system during the time between Kepler 

 and Newton, with which, on the whole, the student 

 of history is familiar, though it is particularly inter- 

 esting to hear on this matter the verdict of an 

 historian who has derived his knowledge so directly 

 and completely from an exhaustive study of the 

 original prints and manuscripts. 



It is difficult to emphasise sufficiently the specific 

 merits of a work of this kind in a brief review. 

 I>oubtless not the least of its many meritorious 

 features is the lucidity and conciseness of exposition. 

 In its endeavour to grasp the essence of the cosmo- 

 gonic ideas the mind is nowhere impeded by an 

 unnecessary accumulation of cumbersome detail. At 

 the same time the non-mathematical reader is sup- 

 NO. 1907, VOL. 74] 



plied with sufficient technical informatton to secure 

 his acquaintance with the principal geometry of the 

 cosmic systems under discussion. This latter advan- 

 tage is important in the case of a work which is 

 clearly not written for a limited circulation among the 

 small section of astronomical experts, but may justly 

 claim to appeal to all who are interested in the history 

 of the general development of scientific culture. 



PRl)F. EHLERS'S ''FESTSCHRIFT." 

 Zeitschrift jiir ■wissenschaftliche Zoologie. Vols. 

 Ixxxii. and Ixxxiii. Festschrift ziir Feier seines 

 siebzigsten Geburtstages am 11 Nov. 1905, Herrn 

 Geheimen Regierungsrat Prof. Ernst Ehlers. 

 Band i., pp. iv + 6g2; Band ii., pp. 741; and plates. 

 (Leipzig : Engelmann, 1905.) 2 vols., price 5L 



THE distinguished zoologist in whose honour 

 these volumes are issued is widely known as 

 an indefatigable worker and one of the most genial 

 of men. Together with the late von Kollilcer, Prof. 

 Ehlers has for many years edited the journal which 

 now celebrates his seventieth birthday. .As a testi- 

 mony of the inspiring character of his teaching and 

 of the regard in which he is held this " Festschrift" 

 gives abundant witness. With no less clearness it 

 indicates the diverse activities of modern zoologists 

 and the particular problems upon which they are 

 engaged. 



With such a varied content, the volumes are 

 difficult to review. The systematic work, admirable 

 as it is, and coordinating or expanding as it does 

 our knowledge of annelids, starfish, and flat-worms, 

 can only be mentioned; nor can we do more than 

 indicate the purport of a few of the many anatomical 

 and physiological papers. 



The place of honour is appropriately given to 

 von Kolliker's paper on the histogenesis of the verte 

 brate nervous system, the last contribution of the 

 master of histology, whose amazing vitality a( 

 eighty-seven years enabled him to conduct research 

 and to discuss difliculties of fact and interpretation 

 with unabated zeal. The month in which this latest 

 defence of the neuron-theory was published brought 

 the tidings that von KoUiker had ceased from work. 



A long and exquisitely illustrated memoir by 

 Vejdowsky gives a minute account of the structure 

 and mode of origin of the annelidan vascular system. 

 The nature of this system in the lower animals has 

 been of late the goal of much research. Under the 

 influence of the trophocoel theory, as stated by Lang 

 on the basis of Bergh's work upon annelids, the 

 vascular system has come to be regarded generally 

 as a mesodermic structure, its cavities as a schizoccel, 

 and not, as had often been suggested, a blastoccelic 

 structure. The results of Vejdowsky's work have led 

 him to a very different conclusion. First he proves, 

 what had often been denied, that annelids possess a 

 vascular endothelium. He finds that this " vaso- 

 thelium " arises in the following way. Blood-vessels 

 are intimately associated with the gut. Their cavi- 

 ties are at first simply a space between the outer 

 ends of the gut-cells and their basal membrane. 

 Into this space cells are budded off from the endo- 



