Ratio of the Electromagnetic to the Electrostatic Unit. 325 



Ball B. 



May 1. Weight in air • • • . 2321*40 g. 



Correction for displaced air 3*20 g. = 2324*60 g. in 



vacuo. 

 May 3. Weight in distilled water, 



ball and sinker ... 208-96 g. at 16°'45 C. 

 Ditto, sinker alone . . . 807-86 g. at 16°-70 C. 



Difference . . . 598'90 

 Correction for air displaced 



by weights . . . . . *09 



598-81 

 Weight of balHn vacuo . 2324' 60 g. 



Loss of weight in water at 



16°-45 C 2923-41 



Ditto, at 4° C 2926-65 = volume in 



cubic centimetres. 



This gives ?*'b = 8'8735. A second determination gave a 

 closely agreeing result. 



In these weighings the bodies were lifted completely out of 

 water, replaced, and air-bubbles carefully removed at least 

 three times in each weighing. The mean of the several 

 values, which differed in the centigrams, was each time taken. 

 These differences were usually due to slight changes in the 

 temperature of the water, the balances being far more 

 sensitive than the thermometer. As, however, the tem- 

 perature was read to ^ of a degree several times during 

 a weighing, and the mean taken, it is thought that the tempe- 

 rature is true to within o, l; and this corresponds in the case 

 of the large ball to about '07 g. I think the values of the 

 radii given above are true to within two or three thousandths 

 of a millimetre. 



Shell. 



The weighings of water contained by the shell were made 

 by replacement. The shell was sealed about the junction of 

 its two halves with white paint, filled with distilled water, and 

 allowed to stand to absorb any air-bubbles which might have 

 escaped the brushing with a wire which was given the inner 

 surface after filling. The condenser was placed on the plat- 

 form of the scales, approximately counterpoised, and then 

 accurately balanced by adding weights to the platform ; about 

 100 c. c. of water was then withdrawn, temperature taken, 

 shell refilled (the space around the opening being thoroughly 



