100 0. N. Rood—Obtaining and measuring very high Vacua 
Reliability of results ; highest vacuum. 
The following are samples of the results obtained. In o 
case sixteen readings were taken in groups of four with the 
following result : 
Exhaustion. 
1 
74 219 139 
78 533 454 
79 = 272 
1 
68 503 182 
Mean aise iahi! 
74 853 449 
Calculating the probable error of the mean with reference to 
abo 
the above four results it is found to be 2-28 per cent of the 
‘quantity seeealy 
hi 
ed. 
igher vacuum measured in the same way gave the fol 
lowing results: 
1 
146 198 800 
1 
175 131 300 
1 
204 081 600 
1 
201 207 200 
; 1 j 
The mean is 178411934’ with a probable error of 5:42 per 
cent of the quantity involved. ive now an extreme case; 
only five single readings were taken ; these corresponded to the 
following exhaustions : 
1 
379 219 500 
1 
371 057 265 
1 
250 941 040 
1 
424 088 232 
1 
691 082 540 
