proceedings: philosophical society 21 



spoke of the behavior of platinum resistance-thermometers under 

 strain. Mr. Burgess referred to the possible change of state of cop- 

 per under pressure. Mr. White spoke of the theoretical considerations 

 involved. Messrs. Hersey and Swann considered the application 

 of the recent theory of electrical conduction to the results. Mr. 

 Wenner stated that the temperature coefficient of coils wound under 

 tension at the Bureau of Standards was generally found different from 

 that of the wire before winding; he noted also that the diagram shown 

 by Mr. Adams for copper is very similar to that obtained for silver at 

 the Bureau. The chair expressed to Mr. Adams the thanks of the 

 Society for the interesting communication. 



Mr. F. Wenner then reported on a research made in collaboration 

 with Mr. C. F. Hanson in a paper entitled The experimental basis for 

 Ohm's law. Some of the experiments which led to the establishment 

 of Ohm's law were discussed and also some of those which were made 

 for the purpose of testing the law. It was pointed out that the ex- 

 perimental tests are not so conclusive as has generally been supposed 

 and that consequently a further consideration of the matter is de- 

 sirable. Using one of the methods devised by Maxwell, results concor- 

 dant to about 1 part in 10 6 were obtained — about five times the accu- 

 racy obtained by Chrystal working under Maxwell's direction. A new 

 method was devised, making use of a combination of a direct and two 

 alternating currents, one with a frequency nearly but not exactly twice 

 that of the other. The maximum value of the resulting, rapidly 

 pulsating current changes in a slow cycle between definite limits, while 

 the average and root mean square values may remain constant. The 

 changing of the maximum value of the current independent of the 

 average value would give changes in the average value of the poten- 

 tial drop, unless the potential drop were strictly proportional to the cur- 

 rent; while keeping the root mean square value of the current con- 

 stant eliminates the disturbances which would result from a slow 

 cyclic change in the heating. Only preliminary measurements have 

 been made, but these give results concordant to about 1 part in 10 8 . 

 In no case has a definite departure from proportionality between 

 current and potential drop been observed. 



The 779th meeting was held on November 25, 1916, at the Cosmos 

 Club. President Briggs in the chair; 38 persons present. The min- 

 utes of the 778th meeting were read in abstract and approved. 



Mr. W. P. White gave a paper, illustrated with lantern slides, on 

 Specific heats at high temperatures. Platinum and certain silicon com- 

 pounds were investigated. The charges were heated, usually in elec- 

 tric heaters, and dropped into water in a calorimeter, so that the 

 heat determination was made at ordinary temperatures under favorable 

 conditions. The high temperature measurements in the furnace, the 

 most critical part of the determinations, were made quite satisfactorily, 

 first, by means of regulators which held the furnace temperature con- 

 stant; second, by measuring temperature at the center of the charge 



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