324 Mr. E. B. Rosa on the Determination o/v, the 



where r, r' are the radii of the shell and ball respectively. 

 The radii are determined by finding the volume of water 

 which fills the shell and which is displaced by the ball. These 

 results are confirmed by direct measurement upon the dividing- 

 engine. 



Ball A. 



May 1.— Weight in air, 2903-83 g. Temperature, 18°*9 ; 

 Bar., 76*0 cm. Volume of ball, 4339 c. c. approximately ; 

 volume of brass weights, 340 c. c. approximately. Correction 

 for displaced air is consequently +4*83 g. .*. weight of 

 ball in vacuo =2908*66 g. A second determination gave 

 2908*64 g. I therefore take for the true weight in vacuo, 

 2908' 65 g. The ball being lighter than water, a sinker was 

 attached and the following weighings made : — 



May 3. Weight in distilled water, 



ball and sinker . . . 210*62 g. at 17 o> 05 C. 

 Ditto, sinker alone . . . 1635*59 g. at 17°* 10 C. 



Difference . . 1424*97 g. 



„ 1425 

 fo r -o~t- c. c. air 

 8*4 



displaced by weights . . *21 



1425 

 Correction for -5-^ c. c. air 

 8*4 



1424*76 

 Weight of ball in vacuo . 2908*65 g. 



Loss of weight in water at 



17°*05 C 4333*41 g. 



Ditto, at 4° C 4338*68 g. = volume in 



cubic centimetres. 



Another determination at a different temperature gave 4338*87. 

 I take as a mean 4338*8, which makes the mean radius 

 / A =10*1180 cm. An error of 0*1 in the number 4338*8 

 would cause an error of less than a thousandth of a millimetre 

 in / A . 



