George Frederic Barker. 231 



science, therefore, it would not be probable that the radio- 

 activity of thorium is a secondary or excited radio-activity due 

 to the uranium associated with it in the minerals previously 

 named." 



Avery instructive address upon " Radio-activity in Chem- 

 istry " was delivered by Dr. Barker before the Chemical 

 Society of Columbia University; it appeared in full in the 

 School of Mines Quarterly (xxiv, 267). It has historical value, 

 and will prove helpful to all wishing to familiarize themselves 

 with the subject. It is accompanied with bibliographies cover- 

 ing 90 titles by the most prominent investigators in this par- 

 ticular field of research. In 1899, Harper and Bros, issued a 

 small volume of 75 octavo pages on " Rontgen Rays," in which 

 are incorporated memoirs by Rontgen, Stokes, and J. J, 

 Thomson, translated and edited by Dr. Barker. 



On the 27th of May, 1893, the American Philosophical 

 Society celebrated the 150th anniversary of its foundation, on 

 which occasion Dr. Barker offered a paper on " Electrical 

 Progress since 1743." This paper is a review of the advances 

 in Physics since that early date, emphasizing in particular the 

 contributions to electrical science by such persons as the 

 immortal founder of the Society, Benjamin Franklin, and by 

 Kinnersley, Robert Hare, Joseph Henry, Joseph _ Saxton, 

 David Rittenhouse, and Alexander D. Bache. " The labors of 

 these men have mightly contributed to advance the develop- 

 ment of scientific thought throughout the world, and so to 

 bring about that exceptional evolution of electrical facts and 

 theories which is the distinguishing feature of the science of 

 the nineteenth century." This little brochure is indeed worthy 

 of study by every student of the physical sciences. 



Still other coriimunications of Dr. Barker are " On the 

 Henry Draper Memorial Photographs of Stellar Spectra " 

 ( Amer. Phil. Soc. xxiv, p. 166) , " On the Use of Carbon 

 Bisulphide in Prisms," (this Journal (3), xxix, 269), in which 

 communication there is presented to the public the observa- 

 tions of his friend. Dr. Henry Draper, taken from the notes of 

 the latter after his death ; and " The Microphone of Hughes " 

 (ibid. (3), xvi, 60), in which Dr. Barker takes occasion to say 

 that the results obtained by Huglies had been clearly antici- 

 pated by more than a year by those of Edison. 



Biographical memoirs of Fi'ederick Augustus Genth, of 

 Henry Draper, of John William Draper, and of M. Carey Lea 

 were written for the National Academy by Di". Barker, and he 

 also prepared for the Smithsonian Institution annual reports 

 upon Physics from the year 1881 to 1885, inclusive. These 

 amount to 253 pages and represent the most recent advanced 

 in the science during these years. 



