with a modified form of Sprengel-pump. 99 
Leakage.—We come now to one of the most important ele- 
ments in the production of high vacua. After the air is de- 
tached from the walls of the pump the leakage Geeanes and 
remains nearly constant. I give below a table of leakages, the 
pump being in each case in a condition suitable for the produc- 
tion of a very high vacuum : 
Duration of the Leakage per hour in cubic 
riment. mm., press. 760™™, 
184 houres. 22 vot 000853 
Ours. 2.0 7: ...°001565 
264 nour “000791 
Hhouree 622s. "000842 
10 (ROU eh 000951 
10> hour 5050.45 2001857 
1 Gaye. 25.00, 001000 
7 ORB coccrweaucn soy 001574 
AVerage:. 2.555 001266 
I endeavored to locate this leakage, and proved that one- 
quarter of it is due to air that enters the gauge from the top of 
its column of mercury, thus: 
Duration of the Gauge-leakage per hour in cubic 
experimen mm., press. 760™™, 
1S boars 20 “Se 7ye 0002299 
TGQQR Cc Wace ee *0004093 
7 GSVOi Ee ees 0003464 
AVORAPE Tose: 0003285 
This renders it very probable that the remaining three- i isa 
ters are due to air given off from the mercury at g. 4, fro 
that i < the bends and at the entrance of the fall-tabe O, ‘fig. 3. 
er on some evidence will be given that renders it prob- 
able that the leakage of the pump when in action is about four 
times as great as the total leakage in a state of rest. 
would in a year amount to °488 cubic millimeters press. 76 60m, 
and ina ee of the above dimensions would exert a pres- 
sure of -0233™™ 
