REVIEWS 343 



Prof. D'Arcy W. Thompson contributes a scholarly and interesting chapter on 

 the Pycnogonida, of which the affinities were discussed recently in Science 

 Progress (Vol. iii., 1909 ; pp. 687-93). He adopts the view, which was contested 

 in the article referred to, that the recently discovered ten-legged forms, Dccolopoda 

 and Petttanympho)i, are the most primitive members of the group. A pleasing 

 feature of this chapter is the prominence given to the observations of the older 

 naturalists. A distinguished zoologist recently told the reviewer that " one never 

 needs to refer to the older writers now except for purposes of nomenclature." This 

 opinion is evidently not shared by Prof. Thompson, who finds the accurate 

 descriptions and acute comments of Linnaeus, Briinnich, and O. Fabricius still 

 worth quotation from the century before last. Not much of importance relating 

 to the Pycnogonida has escaped notice in this chapter, but there seems to be no 

 mention of the fact that some deep-sea species are known to be phosphorescent. 



W. T. Calman. 



Microscopy : The Construction, Use, and Theory of the Microscope. By 



E. J. SPITTA. [Pp. xxii + 502, 16 plates.] (London: John Murray; 2nd 

 edition, 1909. Price 12.?. bd. net.) 



The first edition of this book appeared in August 1907, and the early issue of a 

 new edition indicates a well-deserved popularity. The aim of the author has 

 been to give a clear and useful account of the whole subject, and though this 

 is a somewhat difficult task in a book of this size, Mr. Spitta has succeeded 

 very well. But it is the practical rather than the theoretical side that is promi- 

 nently brought out ; this book will enable the student to obtain an intelligent 

 grasp and will lead him to a skilful manipulation of that beautiful instrument — 

 the microscope. Mr. Spitta is an authoiity on his subject, and his wide practical 

 experience is obvious throughout the book, which abounds in useful hints. To any 

 one desiring a reliable and serviceable guide to the microscope, whether he be 

 a microscopist or merely using the instrument as an aid to work in some other 

 branch of science, we can recommend the book. 



A few words may be said on one or two important features. The value of 

 Mr. Spitta's work is increased by numerous excellent illustrations and plates ; any 

 small difficulty that may be experienced in the text is easily overcome with the 

 assistance of these figures. For permission to use many of the diagrams, the 

 author is indebted to several firms of optical instrument makers, and perhaps, 

 under such circumstances, a suspicion of advertisement is unavoidable. 



The author has wisely refrained from using a large amount of mathematical 

 work in the body of the book, though, where necessary, it has been introduced. 

 In every case, moreover, the physical interpretation is clearly brought before the 

 reader. Mr. Conrady has contributed two chapters, one on the undulatory 

 theory of light, the other on the various theories of microscopic vision. The 

 theories of Airy, Abbe, Altmann, and Stoney are discussed ; and emphasis is 

 laid on the differences between the case of the telescope and that of the microscope, 

 arising from the fact that in the former the objects examined are usually self- 

 luminous, while in the latter they have to be in some way illuminated. The 

 insufficiency of Airy's "spurious disc method" is insisted upon. In a simple, 

 yet fairly comprehensive manner, Abbe's experiments, which at one time were so 

 vigorously attacked— largely, it may be said, on account of the critics' ignorance of 

 the subject — are described, and the work of that physicist vindicated. 



Two subjects, somewhat difficult and often neglected in books of this kind, are 



