( 220 ) 



stop-cock A'2 simt) pressure into tlie lower cylinder, the gas in the 

 closed space between the upper meniscus in i'o and the lower meniscus 

 in the preceding manometer will be compressed and consequently 

 the lower meniscus in By will be further depressed. A similar 

 displacement is repeated in all preceding manometertubes at the 

 adjustment of each following manometertube. If finally we want 

 to get the desired adjustment in all cylinders we must begin because 

 the spaces between two manometers are not provided with separate 

 stop-cocks for drawing off so as not to add unnecessarily to the num- 

 ber of stop-cocks and connecting pieces, by causing the mercury to 

 rise in the manometer to less than the required height i.e. only so 

 far that it will be brought to the required height by tiie following 

 adjustments iu the other tubes. In order to facilitate the filling these 

 heights have been indicated by distinct marks (comp. s-j, x^ in fig. 1). 



In order to bring the apparatus to a given pressure, (at 46 V* 

 atmospheres f.i. as in the drawing) we must find out which multiple 

 of the whole height is nearest to that pressure, how many tubes 

 of the type B we shall have to use therefore and which additional 

 pressure has to be adjusted in A. 



Then all stopcocks except -A'q, KA and X, are opened wide and 

 gas is carefully admitted through X until the difference of level in 

 A has the required amount (in this case 2V4 atmospheres) within 

 about C C.M., after which X is shut. In all the other manometer- 

 tubes the pressure rises to the same height, but the position of the 

 mercury remains unaltered during this process. Then shut A'l ami 

 open X carefully until the mercury in 7?i has reached :'■, ; shut 

 K^ {x is shut) and admit gas through X until the mercury in 7>j 

 has reached ;ro, etc. until the mercury in i?i„ has reached ^j^, shut 

 X and /fji and admit pressure through X till the topsurface of the 

 mercury in D^^ in this special case is just in the middle of the 

 upper cylinder. Then the menisci in all the preceding manometer- 

 tubes are in a proper pcsition. 



A given pressure can always be adjusted accurately within a 

 small fraction of an atmosphere. 



If differences should remain or arise between the pressure adjus- 

 ted and the pressure we want to determine, we can take away these 

 differences by means of the differential tube C which in the 

 case represented here was not used. K^^ to /vjs are left open, 

 A'jc is shut and more gas is admitted through X, but at the same time 

 we draw off through KA just as much as to leave the menisci in ^11 

 in the same position, and then the desired difference of pressure in 

 C is adjusted. After this X and K A are shut. 



