January 9, 1914] 



SCIENCE 



43 



ratory can afford him. As for meteorology 

 or cosmical physics, it has no instruments 

 except those of the physical laboratory. 



But even outside of the purely physical 

 sciences, we see the application of their 

 methods of experimentation. In the phys- 

 iological laboratory we find not only ther- 

 mometers, but accurate manometers for 

 the measurement of the blood pressure, and 

 registering instruments for all the rhythms 

 of the various organs and the study of 

 fatigue, with electroscopes and galvanom- 

 eters for the study of the electrical phe- 

 nomena connected with the nerves and 

 muscles. In fact the fertile brain of the 

 physiologist Einthoven has given back to 

 the physicist the most sensitive galvanom- 

 eter that he possesses in the beautiful 

 string-galvanometer which is used to study 

 the action of the heart by means of the 

 electric currents connected with its beating. 



The science of botany is one that in many 

 of its methods seems very remote from 

 physics, and the work of the systematic 

 botanist whose main interest seems to be 

 to collect and label different plants and file 

 them away in herbaria seems the antip- 

 odes of the methods of the physicist. And 

 yet we have now the subject of plant phys- 

 iology, in the laboratories of which we 

 see again the familiar physical instruments 

 in new applications. But recently in such 

 a laboratory I saw an artificial tree, con- 

 structed of glass tubes and porous porce- 

 lain, which raised water from a reservoir 

 and evaporated it into the air in close imi- 

 tation of a real tree. Here again the ther- 

 mometer and hygrometer are of prime im- 

 portance, while we may expect the calorim- 

 eter, which has become so very important 

 in physiology in connection with nutrition, 

 to play its part in botany as well. It is of 

 interest to find that the direction of the 

 vertical, which seems to be so important 

 in connection with the growth of plants, is 

 not mysterious, but that if the plant is 



subjected to centripetal acceleration in a 

 whirling machine, its root will yield exactly 

 as to gravity. Finally we must credit to 

 botany the study of osmotic pressure, the 

 laws of which as discovered by Pfeffer have 

 opened an enormous field to the physicist 

 and chemist. 



Finally invading the domain of the 

 mental sciences, we find in the laboratory 

 of experimental psychology, which may be 

 variously termed physiological psychology 

 or psychophysics, the same physical in- 

 strument and new ways of applying them. 

 However color is interpreted to the brain 

 by means of the physical and physio- 

 logical mechanism of the eye, its physi- 

 cal properties must be definitely deter- 

 mined before any progress can be made. 

 Similarly the sense of hearing can not be 

 examined with definiteness until physical 

 standards of sound are forthcoming. The 

 slight advance made in the study of the 

 sense of smell is probably due to the lack 

 of its specification in chemical or physical 

 terms. And the favorite subject of study 

 in this field, that of the time of transmis- 

 sion of nerve impulses or of the formation 

 of judgments, depends on the most funda- 

 mental of physical instruments, the clock. 



But it would be tedious, as well as un- 

 necessary, to attempt to enumerate all the 

 instruments that have been contributed to 

 the other sciences by physics. Let us turn 

 to the methods of investigation which have 

 proved characteristic of physical science. 

 The collection of examples of phenomena, 

 and their arrangement in classes, is of 

 course characteristic of all the sciences, of 

 botany or of anthropology as of physics. 

 But the essential idea in classification in 

 physics is the quantitative method, which 

 results in methods of measurement, and the 

 invention of instruments for their per- 

 formance. After this has become possible, 

 the next step is to formulate a theory, 

 which may be of two kinds, either an ex- 



