AT KEW OBSERVATORY AND THEIR DISCUSSION. 



485 



is no clear tendency in the ratios to increase or decrease as the time increases from 

 5 to 60 minutes. There would thus appear to be a very vital distinction between 

 the influence of a stoppage and that of a reduction in the rate of fall of pressure. In 

 both cases there is a reduction in the creep observed in a given time while the 

 pressure is maintained steady at its lowest point, but the stoppage has apparently 

 no appreciable influence on the law of variation of the creep with the time, while the 

 reduction of the rate of fall of pressure has a notable influence in this direction. 



38. The influence of a stoppage is also brought out in an instructive way by 

 comparing the differences of the descending and ascending readings at points below 

 and at points above the stationary pressure with the corresponding data from experi- 

 ments of the normal type. Taking us standards the normal experiments 63 and 66, 

 I have instituted this comparison for experiments 62 and 67, 64 and 65, 68, 69, 70, 

 and exhibit the results in Table XXXIX. The following example will show how 

 the results were arrived at and what they signify. 



The mean of the experiments 63 and 66 gave, in the case of aneroid No. 4, for the 

 sum of the differences, descending less ascending readings, from 15 to 18 inches 

 inclusive '605 inch, and from 18 to 30 inches inclusive 2'635 inches. Now in 

 experiment 69, with a prolonged subsidiary stoppage at 18 inches, the sum of the 

 differences at 15, 16, 17 and 18 inches (after stoppage in descent) was "26 inch, while 

 the sum of the differences at 18 inches (before stoppage in descent) and 19 to 30 inches 

 inclusive was 3'19 inches. Thus stoppage for 20 hours at 18 inches diminished the 

 sum of the differences below this point by 100 ('605 '26) -f- '605, or 57 per cent., 

 and raised the sum of the differences above this point by 100 (3'19 2'635) -f-2'035, 

 or 21 per cent. 



TABLE XXXIX. Percentage Change in Sum of Differences, Descending less 

 Ascending Readings, Below and Above Pressure of Stoppage (+ gain, loss). 



The percentage loss in the sum of the differences below the stationary pressure is, 



