230 George Frederic Barker. 



posed vital. Physiology is daily assuming more and more the 

 character of an applied science. Every action jierformed by the 

 living body is sooner or later, apparently, to be pronounced 

 chemical or physical. And when the last vestige of the vital 

 principle as an independent entity shall disappear from the ter- 

 minology of science, the word "Life," if it remain at all, will 

 remain only to signify, as a collective term, the sum of the phe- 

 nomena exhibited by an active organized or organic being." 



In following the career of our friend there is plainly seen a 

 versatility on his part, as well as a keen interest for other 

 branches of science than that one to which he gave the best 

 years of his life. Thus, he is found a member of an expedition 

 to Kawlings, Wyoming, for the purpose of reporting "• On the 

 Total Solar Eclipse of July 29, 1878"; liis particular di^ty 

 being- to observe with an analyzing spectroscope the presence, 

 either of light, or of dark (Fraunhofer), lines in the spectrum 

 of the corona. (See Proc. Amer. Phil. Soc, xviii, 1880.) 

 Again, in connection with Professor Kowland, he reported 

 ''On the Efficiency of Edison's Electric Light." See this 

 Journal (3), xix, 337. 



Dr. Barker was the first person to exhibit radium in this 

 country (189-1) after its isolation by Madame Curie in Paris. 

 Radio-activity appealed so strongly to him, that it is not sur- 

 prising to find a paper of his on ''Padio-activity of Thorium 

 Minerals" in tliis Journal ( (1)', xvi, 101, 1903). In this com- 

 munication, the autiior introduces a number of original contri- 

 butions. He repealed tlie experiments of Hofmann and Zer- 

 ban, relative to the i-adio-activity of Brazilian monazite, which 

 contains no uranium, and confirmed the results of these observ- 

 ers, to wit : that the thorium from this monazite is probably 

 radio-active. From a series of experiments, he further con- 

 cluded that thorium is a primary radio-active substance, and 

 added that the thorium emanation rapidly decays, falling to 

 one-half its value in one minute, while that of the radium 

 emanation retains its active properties for several weeks. On 

 the other hand, the excited radio-activity produced by the 

 former emanation is much more prominent than that pro-" 

 duced by the latter. Since excited radio-activity can be pro- 

 duced on bodies if the emanation be present, even in the 

 absence of a radio-active substance, and since the amount of 

 effect is directly proportional to the amount of emanation, it 

 follow^s, first, that the production of excited radio-activity is a 

 property of the emanation, and, therefore, is also produced in 

 bodies where the radio-active emanations from thorium aud 

 radium are present : and second, that uranium and polonium, 

 which do not give. forth any emanation, do not possess the 

 power of exciting radio-activity. In the present view of 



