AT KEW OBSERVATORY AND THEIR DISCUSSION. 



481 



In the first two groups there was in two out of the three experiments a subsidiary 

 stoppage of 1 hour at a pressure above the lowest. In the third group there was a 

 subsidiary stoppage of about 26 hours' duration in all three experiments. As the 

 order of the experiments is of significance, I give particulars : 



As experiments Nos. 63 and 66 were of the normal type, so far as descending 

 readings are concerned, I have used them as a standard to which to refer the others. 

 To see, for instance, how an hour's stoppage at 18 inches influences the reading when 

 the pressure 15 inches is reached, I compare the mean error at 15 less the mean 

 error at 18, prior to the stoppage, in experiments 62 and 67, with the mean 

 difference between the errors at 15 and 18 in experiments 63 and 66. For instance, 

 in aneroid No. 4, I found : 



from experiments 62 and 67, mean error (before stoppage) at 18 = -|- '01, 

 62 and 67, .. .. at 15 = -f '015, 



and so error at 15 less error at 18 = + '005 ; 



from experiments 63 and 66, mean error . . . . at 18 + '01, 



63 and 66, .. .. at 15 = -f '04, 



and so error at 15 less error at 1 8 ~ + '03. 



Thus an hour's stoppage at 18 has lowered the reading at 15 by 



03 '005, or '025 inch. 



Again, to determine the influence of the above stoppage on the total creep which 

 takes place as pressure is being lowered from 18 to 15, I compare the mean error at 

 15 less the mean error at 18, subsequent to the stoppage, in experiments 62 and 67 

 with the difference between the mean errors at 15 and 18 in experiments 63 and 66. 

 For instance, in aneroid No. 4, 



from experiments 62 and 67, mean error (after stoppage) at 18 = '06, 

 62 and 67, .. .. at 15 = + '015, 



and so error at 15 less error at 18 = + '075 ; 

 YOL. cxci, A. 3 Q 



