AT KEW OBSERVATORY AND THEIR DISCUSSION. 



479 



The ratios would seem to be somewhat above their average near the centre of the 

 range, and below it at both extremities ; but there are hardly sufficient experiments 

 to justify any too positive conclusion. That the mean ratio is less than unity is 

 absolutely clear ; and there can be but little doubt that this is due to the fact that 

 the stoppage at the lowest point in the case of the slower experiments was not 

 doubled along with the other time intervals. 



I likewise compared experiments Nos. 27 and 28 over the longest range, 30-15 

 inches, at the slower rate, 1 inch in 10 minutes, with earlier experiments, Nos. 10, 

 11, 14, 15, over the same range at the normal rate. Only one aneroid, No. 4, was 

 available for calculation, owing to erratic behaviour in No. 1. It will thus suffice to 

 mention that the results obtained were analogous to those in Table XXXIV., and 

 that for the ratio of the sums of the differences of the descending and ascending 

 readings at the two different rates I found 



case 1 inch in 10 minutes 

 case 1 inch in 5 minutes 



In both cases, as already stated, only 10 minutes stoppage was allowed at the 

 lowest pressure. 



33. The influence of the rate of change of pressure on the rate of recovery at the 

 end of a pressure cycle was less exactly ascertained. After experiments in which 

 the pressure changes are slow, the variations observed in the reading during the first 

 hour or two of the recovery are so small as to be largely affected by small errors of 

 reading. After 12 or 24 hours recovery, readings are affected by various sources of 

 uncertainty, e.g., change of temperature or atmospheric pressure, and possible 

 permanent shift of zero. 



Table XXXV. compares the recovery following pressure cycles a.t the two rates 

 1 inch in 10 and 1 inch in 5 minutes. 



The data for the normal rate are taken from Table XVII. , and D,/D has the same 

 meaning as there. The data for the slower rate were obtained from the experiments 

 25, 26, 37, 38 over the range 30-2 L inches. 



TABLE XXXV. Recovery after Pressure Cycle, Values of D ( /D . 



* If No. 4 omitted, only '69. For some reason, reading recorded for No. 4 showed on two occasions 

 apparent fall of '01 inch in interval 15 to 20 minutes. 



