341 



side (c) is : — m.m., it' f =: -7-—^ = 0,051 B. vSiipposo L]) to be the increase 

 g 1 9,38 



of pressure (in m.ni. mereiiiT), necessaryoii the right side, to sink the 



mercury-surface just J m.m. The mer- 

 -iip cnry-surface on tlie left side, will then 

 rise just 1 m.m., and the octane- 

 column from (' to c' (=: L h m.m.), 



D 



over — m. m. The difference ot level 

 d 



of the two mercnry-surfaces is now: 



[a — 2) m.m., and the octtme-column 



fa D\ 



to the left = 1 -1 — 1 mm. This 



V e d 



or 



corresponds to a mercury -column of: 

 'd 



^— 1 



8 = a 



f -| — im.m. 



d 



Therefore the necessary increase 

 of pressure on the right side {= A p), 

 is evidently : 



[a — £ + —«] — (a— 2) m.m. = 2 + 

 -\- 3 [ 1 I m.m., and thus : 



D 



+ M 1 



•a^M-.-.^. 



d 



Ap^ 8 + (2-.)- I X AA. 



The reciprocal of the expression between 1 1 will be seen to be 

 the "multiplication factor" F of the instrument. With small values of 

 e. (2— f) will ditfer little from 2 ; therefore it is necessary to reduce 



— as much as possible and to make F as large as possible. 



In our instrument these conditions were fulfilled in the following 

 way : preliminary experiment gave d ■= 2,406 m.m', and D = 1257,36 



m.m'; thus — = 0,00191, and i^ becomes ca. 18. The reproducibility 



of the same pressure appeared to be possible within a limit of 



23 

 Proceedings Royal Acad. Amsterdam. Vol. XVII. 



