proceedings: philosophical society 559 



vapor phases. Two types of furnaces were operated, to show the 

 production of very high temperatures. The advantage of using the 

 cascade principle of heating was explained and a tungsten wire 1 mm. 

 in diameter was melted in the cascade attachment to the larger model 

 furnace exhibited. It was pointed out that temperatures up to 1680°C. 

 may be accurately measured by means of the speaker's new type tin 

 pyrometer which makes use of the property possessed by molten tin 

 of increasing in resistance linearly with the temperature. 



The characteristic facts of metallic conduction over a wide range 

 of temperature were explained and several curves were thrown on the 

 screen. The peculiarities of the electrical conduction of hot gases were 

 described and it was explained how the unstable character of gas con- 

 duction at very high temperature may be used to make a small fur- 

 nace act in the capacity of a telephone receiver and talk. The com- 

 monly accepted "free electron theory" of metallic conduction was ex- 

 plained and reasons given why the theory appears quite inadeciuate 

 to account for experimental facts. A new hypothesis, which the 

 speaker called the '"electric transport theory" of conduction, was 

 briefly explained. The lecture concluded with a plea for employing 

 experimental methods of investigation in acquiring new knowledge of 

 the properties of matter under all temperature conditions. As a final 

 experiment an electromagnetic piece of apparatus which the speaT^er 

 called "an electric Jack-in-the-box," was shown. 



The Chair expressed to Professor Northrup the appreciation and 

 thanks of the meml^ers of the Society and guests present for his inter- 

 esting and instructive lecture and experiments. 



The 758th meeting was held on May 22, 1915, at the Cosmos Club, 

 President Eichelberger in the chair; 30 persons present. 



Mr. C. E. Van Orstrand presented a paper by himself and Mr. 

 F. P. Dewey entitled Preliminary report on the diffusion of solids. 

 The coefficients of diffusion of gold into lead at temperatures of 100°, 

 150°, and 197°C. were found to be in close agreement with values ob- 

 tained by Roberts-Austen. Preliminary tests on the variation with 

 pressure of the coefficients of diffusion of gold into lead were not conclu- 

 sive, but point to the possibility that the coefficient is increased. Va- 

 rious methods of determining the constants of the Fourier integral which 

 represents the dift'usion of heat and of. substances in solution were chs- 

 cussed for the case of constant initial quality. The exceptional agree- 

 ment between the observed and theoretical curves was emphasized. 

 The paper was cUscussed by Messrs. Humphreys and Swann. 



Mr. H. C Dickinson then spoke on The specific heat of ice at tem- 

 peratures near the melting point, presenting results obtained in co- 

 operation with Mr. N. S. Osborne. (PubHshed in the Journal of the 

 Washington Academy of Sciences, 5: 338-340. 1915.) 



Mr. W. D. Lambert then spoke on An exact formula for theoretical 

 gravity at the earth's surface. The mathematical expressions usually 

 given for the force of gravity at the earth's surface constitute only 2 



