')12 



the lueasiiring tube should be takea into account. The gauging takes 

 place at 1 atni. ; during the meastirement the tube is subjected to 

 a pressure on all sides, in consequence of which the volume decreases. 

 As the correction in question is only a small one, we have thought 

 that tbi' onr tirst cah'idalions it would suffice if we took the com- 

 pressibility of our glass equal (o the value delerniined by Amaoat. 

 We have therefore put the factor of compressibility at 22 X 10^" 

 and assumed this quantity to be constant between 1 and 2500 atms. 



Also to the values of the pressure read directly some corrections 

 should be applied. The weights in kg. read on the pressure balance 

 shoidd first be reduced to kg. per cm", by taking the value of the 

 effective area into account. In anticipation of the comparison of the 

 small pressure balance with an open manometer of sufficient capa- 

 city discussed in Comm. N". 5 p. 759, we have assumed that the 

 effective area of the small balance, the piston of which is as 

 accurately as possible ground in at 1 cm^, really amounts to 1 cm^ 



Since we- wrote our first communication we have been greatly 

 strengthened in the conviction that we cannot make great errors in 

 this way, l»y the result of Gkorg Ki.kin's i-esearch ^). According to 

 his investigations') the error in consequence of the neglect of the 

 difference between piston and cylindei" sections for Schaffer and 

 Budknberg's balance amounts '.o at most O.!"/,,,., and the deviation of 

 the indicated and the directly measured value of the difference of 

 the two piston sections is OA^/^q in the case examined by him. 



Now the large pressure balance could be conipared with the small 

 pressure balance by measuring the same point of the isotherm in 

 the neighbourhood of 250 atms. first with the one, and then with 

 the other. So the measuring tube with the galvanometer in connection 

 with it etc. serves simply as a manoscope, to judge when in the 

 use of the two balances the pressure is exact!}' equal. It then appeared 

 from some observations carried out in this way that when the section 

 of the small balance is put at == 1 cm'., the section of the small 

 head of the large balance must also be put at 1 cm', within the 

 limits of the errors of observation. As at these pressures the ei-rors 

 of observation are vei-y small as we saw above, and will certainly 

 remain below 0,2°/^^^, this result is a new confirmation of the great 

 accuracy of the Schaffer and Budp;nbkrg pressure balances, and it 

 gives therefore a new support to the validity of the made supposition. 



In the same way a comparison was made between the small and 



^) Untersuctiung unci Kritik von Hochdrucknnessern. Berlin 1909, 

 ~) Loc. cit. p. -17. 



