868 



SCIENCE 



[N. S. Vol. XXVI. No. 677 



NEW YOEK 



The American Mathematical Society. — December 

 27, 28. President, Professor H. S. White, Vassar 

 College; secretary, Professor F. N. Cole, Columbia 

 UniTersity. 



ALBUQUEEQUE, N. M. 



The Oeological Society of America. — December 

 SO-January 4. President, President Charles E. 

 Van Hise, University of Wisconsin; secretary, 

 Dr. Edmund 0. Hovey, American Museum of Nat- 

 ural History, New York City. 



ITHACA 



The American Philosophical Association. — De- 

 cember 26, 28. President, Professor H. N. Gardi- 

 ner, Smith College; secretary, Professor Frank 

 Thilly, Cornell University, Ithaca, N. Y. 



NEXT SUMMEB, AT SOME PLACE TO BE DETEEMINED 



The Astronomical and Astrophysical Society of 

 America. — President, Professor Edward C. Picker- 

 ing, Harvard College Observatory; secretary. Pro- 

 fessor Geo. C. Comstoek, Washburn Observatory, 

 Madison, Wisconsin. 



THE PHILOSOPHICAL SOCIETY OP WASHINGTON 



The 638th meeting of the society was held 

 November 9, 1907, President Hayford in the 

 chair. Mr. 0. E. Waters, of the Bureau of 

 Standards, presented by invitation a paper 

 entitled "The Standard Cell." The speaker 

 reviewed briefly the earlier efforts to fix ade- 

 quate standards of electrical measurements, 

 the unit of resistance having first received 

 attention, mention being made of the work 

 of the British Association in this connection. 

 It was noted that present requirements de- 

 mand higher accuracy in the standards of 

 measurement. The development of the stand- 

 ard cell, dovsTi to the present time, was briefly 

 reviewed and the defects of those formerly 

 used were 'pointed out, especial reference being 

 made of their lack of stability. 



The principal feature in the preparation of 

 a standard cell is that of securing materials 

 of requisite purity. The methods employed 

 to secure satisfactory materials and the results 

 obtained by Messrs. Wolff and Waters at the 

 National Bureau of Standards, in preparing 

 the H type of standard cell were spoken of 

 at considerable length. 



Several chemical compounds were tested in 

 the experiments. The difficulties of obtaining 

 mercurous and cadmium sulphates were espe- 

 cially pointed out, and the methods devised 

 for obtaining them in a sufficiently pure state 

 were described. Before setting up the cells 

 the materials were carefully cleaned. More 

 accordant results were obtained by amalgam- 

 ating the platinum terminals. The cells were 

 measured in an electric bath in order to main- 

 tain a steady temperature. The thermo- 

 electric effects were eliminated by the methods 

 of observation. The experiments showed that 

 mercurous sulphate can be obtained in several 

 ways that will give good electromotive force 

 properties. Standard cells are now found 

 constant enough to be depended upon for a 

 considerable length of time. The final con- 

 clusion was that satisfactory cells can now 

 be set up by different observers of different 

 materials. 



The second paper of the evening was pre- 

 sented by Mr. 0. W. Burrows on "The Re- 

 duction of Iron to a Magnetically Neutral 

 State for Permeability Measurements." In 

 the experiments described several different 

 kinds of iron were used. The test pieces were 

 50 cm. in length and varied in square cross- 

 section from 0.3 mm. to 1 cm. The ballistic 

 method was used in the demagnetization tests. 

 Numerous diagrams were exhibited showing 

 permeability, induction effect, effect of tem- 

 perature and of vibration, and also curves of 

 tests of non-homogeneous iron. 



As a matter of definition iron is in a mag- 

 netically neutral state when it is free from 

 all residual induction and yields as readily to 

 positive as to negative magnetizing forces. A 

 small magnetic needle or a movable test coil 

 will give evidence of any residual induction, 

 but they tell nothing as to any difference in 

 susceptibility to positive and negative forces. 

 A long series of experiments leads to the 

 conclusion that iron is in the neutral state 

 when the change in induction observed on 

 reversal of a given magnetic force is a maxi- 

 mum. Imperfect demagnetization always re- 

 sults in a lower induction. The following 

 points are noted : 



1. The higher the rate of reversal or fre- 



