18 PROCEEDINGS OF THE BOSTON MEETING 



"The isomorphism and thermal properties of the feldspars/' appeared in 

 1904, and contains an introduction written by Dr. Becker, in which the 

 purpose and progress of his thought in this direction is briefly but clearly 

 set forth. 



In this year also the Carnegie Institution of Washington came to the 

 aid of the undertaking and increased both its scope (to include chem- 

 istry) and its resources. In 1907 a separate and more appropriate labora- 

 tory building was provided by the same institution, and here he carried 

 out (in collaboration with Mr. Van Orstrand) the experimental work on 

 schistosity, elasticity, and diffusion which occupied the closing years of 

 his life. The major portion of the results of this later activity is still 

 unpublished. 



He had outlined several papers such as "Elastic after-effect," "Notes 

 pertaining to the probability integral,'' "Applications of capillarity to 

 oil problems," and a "Treatise on geophysics." 



It is greatly to be regretted that the paper on "Elastic after-effect" 

 was not published during Dr. Becker's lifetime. It represents a vast 

 amount of painstaking experimental work by Mr. Van Orstrand and his 

 associates, using the most refined methods known to quantitative physics, 

 and offers, I think, more elaborate as well as more comprehensive data 

 on elastic after-effect than have been obtained hitherto by any investi- 

 gator. It is obviously unfair, not to say inexcusably presumptuous, to 

 forecast the results of the unpublished work of another, but I cannot for- 

 bear directing attention to this paper, when it may appear, because of 

 the value of the data in throwing light upon the vexing subject of the 

 fundamental definition of "solid" and "liquid" and the possibility of 

 placing a boundary between these two states of matter which shall be 

 theoretically sound. The classical definitions of these states of matter 

 were conceived at a period when elastic deformation was much less pre- 

 cisely measurable than now, when the phenomena of plasticity formed a 

 terra incognita, and when the study of the thermal relations between 

 these two states had not been extended to such inert substances as the 

 silicates. The consequent confusion in our conception of these states, 

 according as they happened to be viewed from the mechanical or thermal 

 standpoint, was a problem which interested Dr. Becker profoundly and 

 one to which he devoted himself most assiduously during several of the 

 later years of his life. 



Dr. Becker enjoyed a wide acquaintance and received many honors, 

 both at the hands of his colleagues and of foreign learned bodies. He 

 was elected to the National Academy of Sciences in 1901; also the Presi- 

 dency of the Geological Society of America in 1914. 



