568 RECORD OF MEETINGS OF THE 



tions combine the swimming feet of C. parens and C. brevi- 

 spinosus in the same individual. These facts, together with 

 the frequent replacement of setae by spines, the constant asso- 

 ciation of the forms, and their occasional sequence in small 

 aquaria, indicate a very close relationship among the species 

 observed and suggest that they are transitional forms in the 

 development*of a single species. 



Dr. Wheeler described the structure and ecology of many 

 "ants that raise mushrooms," giving special attention to the 

 species of Texas and Mexico, where his own studies of these 

 ants were made. Numerous lantern slides illustrated this 

 lecture, and at its close many slides from photographs of ants 

 kept in captivity by Miss Adele M. Fielde were exhibited. 



M. A, Bigelow, 



Secretary. 



SECTION OF ASTRONOMY, PHYSICS, AND CHEMISTRY. 



January 23, 1905. 



Section met at 8.15 p.m. at Fayerweather Hall, Columbia 

 University, Vice-President E. R. von Nardroff presiding. 



The minutes of the last meeting of the Section were read and 

 approved. 



The following program was then offered : 



A. P. Wills, The Magnetic Susceptibility of Water. 

 H. C. Parker, Experiments relating to the Conductivity 

 of Powders at High Temperatures. 



Summary of Papers. 



In connection with Dr. Wills's paper, experiments were 

 made with the large electro magnet of Columbia University 

 to determine the magnetic susceptibility of water. With the 

 aid of this magnet, which is one of the largest in existence, Dr. 

 Wills found the coefficient of susceptibility of water to be 

 — 0.72 X 10- 6 , and also to be independent of the field strength 

 over a range from 4,000 to 16,000 C.G.S. units. 



Dr. Parker said that when a conducting powder like graphite 

 is mixed with a non-conducting refractory powder, the resistance 



