102 O. N. Rood— Obtaining and measuring very high Vacua, ete. 
Time necessary for removal Greatest attainable 
+ the air. i 
: ] 
J0 mimites: 220.22. - oe 
5 000 000 
7°5 minutes , 
2 eeatatean it DOR 000 
7 
O-0 NENULCR oo we — 
aaa 12 000 000 
In point of fact the highest exhaustion I ever obtained with 
this pump was 5-37$-s53 from which I infer that the leakage 
I wish, in conclusion, to express my thanks to my assistant, 
Dr. Ihlseng, for the labor he has expended in making the large 
number of computations necessarily involved in work of this 
ind, 
New York, June 10, 1881 
