^v 



THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES. ] 



Aet. I. — On the Pressure Coefficient of Mercury Resistance ; 

 by A. deForest Palmer, Jr. 



During the last fifty years many physicists have investi- 

 gated the specific resistance of mercury and its variations under 

 different conditions, yet the only determinations of the pressure 

 coefficient, previously published, are those of Barus,* who 

 found —*00003 by subjecting commercial mercury to pressures 

 up to 400 atmospheres, and Lenz,f who found — *0002 for pure 

 mercury between one and sixty atmospheres. The discordance 

 of these results is far too great to be explained by impurities 

 in the mercury and invites further study. 



The long range of pressure desired for the present investi- 

 gation was easily obtained with Professor Barus's " Screw 

 compressor." This instrument, together with the vertical 

 piezometer employed in my work, has been so fully described 

 elsewhere J that only a cursory mention is necessary here. The 

 piezometer proper consists of a cold drawn seamless steel tube, 

 about 6 mm internal and 13 mm external diameter and 60 cm long, 

 connected to the compressor in such a manner that very per- 

 fect electrical insulation exists between the two without ren- 

 dering the joint appreciably leaky. The whole apparatus was 

 filled with heavy mineral oil which, though more viscous than 

 water, attained uniformity of pressure with sufficient rapidity 

 and possessed the advantage of being a very good insulator. 



*Barus, this Journal, III, xl, p. 219, 1890. 

 •f-LeDZ, Stuttgart, 1882 ; Wied. Beibl., vi, p. 802, 1882. 



JBarus, Phil. Mag., Oct., 1890, p. 340; Proc. Amer. Acad., xxv, p. 93, 1890; 

 Bull. U. S. Geological Survey, No. 96. 



Am. Jour. Sci.— Fourth Series, Yol. IY, No. 1.— July, 1897. 



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