44+ THE POPULAR SCIENCE MONTHLY. 



a shallow pit scooped in the sand. A man was then put inside to 

 shovel out the sand, and, as he dug, the curb sank around him. Pres- 

 ently he was waist-deep in water, and the well was finished and yielded 

 freely all summer. 



* 



MABEY'S NEW EESULTS IN ANIMAL MOVEMENT S. 



By Pkof. ALFEED M. MAYER, 



OF THE STEVENS INSTITUTE OF TECHNOLOGY. 



THE publication of Marey's "Animal Mechanism" in the "Interna- 

 tional Scientific Series " has put the general reader in possession 

 of one of the most interesting works ever published on experimental 

 physiology. The simplicity and precision of the author's experimental 

 methods, his conscientiousness in being sure of one step before he takes 

 the next, and the skill displayed in interpreting and combining his ex- 

 perimental results all these admirable characteristics have rendered 

 his book instructive and entertaining to those who merely follow from 

 afar the progress of science, while, at the same time, he has furnished 

 a model of precise research and clear exposition to the professed sci- 

 entist. 



Marey arrives at his facts directly, not inferentially, and this is the 

 charm of his book. The mind of the reader does not rest on the fal- 

 lible judgment or mere opinion of the author, but is brought face to 

 face with the very records made by the phenomena themselves. 



In studying the progress of science, one cannot help remarking 

 certain periods of sudden acceleration in the progress of discovery. 

 These periods of unusual activity are not always, but certainly are 

 very often, due to the invention of some precise and readily-applicable 

 instrument, which gives, as it were, a new scientific sense, and brings 

 into the range of our intellectual vision phenomena and numbers 

 whose existence were barely suspected, until revealed by the aid of 

 some comparatively simple contrivance. Such epochs of sudden prog- 

 ress followed the inventions of the telescope, the spectroscope, the 

 ophthalmoscope, the galvanometer, and the tuning-fork chronoscope. 

 For the latter instrument, men of science are indebted to Dr. Thomas 

 Young, that wonderful man, w r ho touched no department of knowledge 

 that he did not adorn. The application of the sinuous traces of a 

 vibrating tuning-fork on a rolling cylinder, to divide a second of time 

 into as many parts as the number of times the fork swings to and fro 

 in a second, was described by Young in 1807, and published in his 

 " Lectures on Natural Philosophy and the Mechanical Arts," vol. i., 

 p. 191. Like Young's discoveries of the theory of colors, and of the 

 undulatory theory of light, this beautiful invention laid fallow for 

 many years, until reinvented in 1840 by Duhamel, and subsequently 

 brought into general use in physics and physiology. It is now the 



