480 



DR. C. CHREE, EXPERIMENTS ON ANEROID BAROMETERS 



The number of experiments at the slower rate was insufficient to give very smooth 

 results, and it would be waste of time to fit a formula to them. We should not be 

 justified in regarding the coincidence between the data under 10 and 20 minutes in 

 the second line with those under 5 and 10 minutes in the first as more than 

 accidental. At the same time there seems conclusive evidence that the rate of 

 recovery becomes slower when the rate of the previous pressure changes is reduced. 



This is further illustrated in Table XXXVI. , which compares the recovery in 

 experiments Nos. 73 and 74 with that exhibited in experiments N'os. 71, 72, and 75. 



TABLE XXXVI. Recovery after Pressure Cycle, values of D</D . 



The uncertainties referred to above as unavoidable in a small number of experi- 

 ments of this kind are conspicuous in Table XXXVI. ; but as to the recovery being 

 very much slower in the experiments with the slow pressure change there is no 

 room for doubt. That it is exactly or almost exactly nine times as slow in the one 

 case as in the other is a conclusion for which the evidence is insufficient ; but there 

 is at least nothing to demonstrate the contrary. The observations in the case of 

 the experiments at the slower rate would naturally have been taken at the 

 intervals 45, 90, 135, &c., minutes after return to atmospheric pressure, but daylight 

 did not last long enough to admit of this. The extreme slowness of recovery after 

 experiments such as Nos. 73 and 74 is a somewhat serious obstacle to research. 



Effects of Stoppage. 



34. The influence of a stoppage on the readings at lower pressures is shown by 

 three groups, each of three experiments, in all of which pressure was reduced at the 

 rate of 1 inch in 5 minutes in most cases with a subsidiary stoppage to 15 inches, 

 and maintained at that point for an hour. 



