GEORGE FREDERICK BARKER. xvii 



and conscientious. His text-book on " Elementary Chemistry " 

 which first appeared in 1870 went through many editions, and was 

 esteemed as embodying the most advanced thought, presented for 

 the first time in our language thoroughly and systematically. No 

 less an authority than Wolcott Gibbs commended the book highly. 



Barker's '"Physics, Advanced Course" published in 1892 as one 

 of the American Science Series, was likewise an embodiment of the 

 most modern views and met with a hearty reception. The treatment 

 was mainly from the standpoint of energy and interchanges therein. 

 and the ether of space was frankly assumed as the fundamental 

 thing in dealing with all forms of radiation. From his habit of 

 mind it was to be expected that in his scientific papers we should 

 also find the results of the latest investigations. He was particular in 

 giving a comprehensive bibliography of the subject, where it was 

 possible. Thus, the valuable address delivered by him before the 

 Chemical Society at Columbia University in March, 1903, is a model 

 paper. Its subject was " Radio-Activity and Chemistry." and its 

 great historical value will be understood when it is stated that to it 

 is appended a bibliography of no less than ninety titles of papers 

 by the leading investigators. 



Some of his earlier papers and addressess assisted to a con- 

 siderable degree in enforcing the great principles of conservation 

 and correlation of forces, the discussion of which was carried on 

 actively in the period between i860 and 1880. Before those years 

 the ideas of permanence of energy and the importance of energy 

 interchanges had not received universal recognition or acceptance. 

 It is now generally recognized that the indestructibility of energy is 

 a more necessary postulate than the indestructibility of matter. 



Dr. Barker's logical mind did not limit itself to the considera- 

 tion of physical forces merely. He had taken the degree of doctor 

 of medicine and it was natural that he should be led to consider the 

 relations between the physical and so-called vital forces. We find 

 his views expressed in a paper entitled " The Correlation of \^ital 

 and Physical Forces," published in 1875 by Van Nostrand, and also 

 in his address as retiring president of the American Association for 

 the Advancement of Science, at the Boston meeting in 1882. This 



PROC. AMER. PHIL. SOC. L. I99*, PRINTED JULY I, I9II. 



