98 O. N. Rood—Obtaining and measuring very high Vacua 
increase sensibly, when the exhausted pump and gauge are 
allowed to stand unused for twenty days 
Rate of the pump’s work.—It is quite important to know the 
rate of the pump at different degrees of exhaustion, for the pur- 
pose of enabling the experimenter to produce a definite exhaus- 
tion with facility ; also if its maximum rate is known and the 
minimum rate of leakage, it becomes possible to oo the 
highest vacuum oo with the instrument. amples 
are given in the tables below: the total capacity was ie abe 
100, 000 cubic mm. 
Time. exhaustion. Ratio. 
78 4511 1 
10 minutes Seni sacs oh) sa gel dong sume 
1 3°53 
276 980 | 
1h Gn Oe So. bio e 
1 6°10 
1 687 140 } 
10 Mn OP es. Bs 
1 4°15 
7 002 000 
Upon another occasion the following rates and exhaustions 
were obtaine 
Time. Exhaustion. Rate. 
7 812500 1 
Ty oiites se ee i ee 
| 3°18 
24 875 620 1 
10 mites a | ee 
] 2°69 
67 024 090 : 
10 minutes Ce Oe tes 
1 122 
81 760 810 1 
10 mins ee te 
1 1°67 
136 986 300 ‘ 
10 wie 8 peice 
1°23 
1 
170 648 500 
The irregular variations in the rates are due to the mode in 
which the flow of the mercury was in each case regulated. 
