42 



THE AMERICAN NATURALIST [Vol. XLI 



Another interesting feature of these books is the free use which is 

 made in quahtative explanations of such conceptions as the kinetic 

 theory of gases, the ionic theory of electrolytic conduction, and the 

 wave front in geometrical optics. Whether or not it pays, for instance, 

 to displace the old ray-optics, which must, of course, be properly 

 interpreted, by the more valuable but also more difficult notion of 

 the wave front, is a question of pedagogy which each teacher must 

 decide for himself. Fortunately the treatment of the most danger- 

 ously spectacular part of our modern physics is confined to the last 

 twelve pages of the text-book, where there is an account, admirable 

 as regards both interest and conservatism, of vacuum tube phenomena 

 and of radio-activity, including some of the evidence for the existence 

 of electrons, together with brief statements of the corpuscular theory 

 of matter and of the disintegration theory of radio-activity. 



Many other features, while not unique, are nevertheless worthy of 

 much praise. For instance, the experiments, both for the laboratory 

 and for the lecture room, are ingeniously simple and yet, so far as one 

 oan judge without trying them, entirely effective. 



The typography is good, and the illustrations are most excellent, 

 both in technique and in conception; and the sixteen full-page half- 

 tones of eminent physicists, each with a short paragraph describing 

 the man's life and work, are a notable addition not only to the attrac- 

 tiveness but to the real value of the books. 



H. N. D. 



BIOLOGY. 



Jennings' Behavior of the Lower Organisms.^ — It is now nearly 

 a decade since Professor Jennings published his first brochure on 

 the reactions to stimuli in unicellular organisms. The intervening 

 period has been one of continuous activity on his part in the study 

 of animal behavior, especially aiiioiii,^ the lower organisms. His 

 investigations have not been strictly ((.iifiiKMl lo the Protozoa for 

 among the score or more of titles of inipoitaiit contributions from his 



' H. S. Jennings. Behavior of the Lower Organiams. Columbia University. 

 Biological Series, New York, The Macmillan Co., 1906, 8vo. xiv + 366 pp., 

 illus. $3.00. 



