498 DR. C. CHREE, EXPERIMENTS ON ANEROID BAROMETERS 



Evidently, little weight attaches to individual results after a week's recovery, A 

 small permanent change or a slight initial fatigue in an aneroid would have a large 

 effect on the final data. Even after a day's rest the results are somewhat erratic. 



So far as one can judge from the recovery during the first hour, the lowness of 

 the pressure to which the aneroids were exposed was immaterial. There is certainly 

 no indication of the recovery becoming slower as the stationary pressure is more 

 remote from 30 inches. It must be remembered, of course, that the aneroids 

 exposed to the different pressures were different, so that individual peculiarities 

 were not eliminated. 



Comparing Table XL VIII. with Tables XVII. and XXXVI. , it will be seen that 

 the rate of recovery in Mr. WHYMPER'S experiments was slower than in the case of 

 the normal Kew experiments, but faster than in those experiments where pressure 

 was reduced at the rate of an inch in 45 minutes, and where the lowest pressure was 

 maintained stationary for 18 hours. 



53. There are other data on Mr. WHYMPER'S p. 33 relating to the recovery of 

 22 aneroids, which had been exposed for a week to a pressure of 21 '692 inches. 

 These data I have not considered, for the reason that the reading during recovery 

 proved higher than the reading prior to the experiment in 



1 aneroid on return to atmospheric pressure, 

 5 aneroids 14 hours after return to atmospheric pressure, 

 9 12 days 

 1" 30 ,, ,, ,, ,, 



Such a wholesale tendency to a rise of zero, whatever its cause, would have 

 introduced great uncertainty into any conclusions drawn, even as to the recovery 

 during the first 14 hours, the shortest interval for which results are given. 



54. Part 3 of Mr. WHYMPER'S pamphlet, dealing with the "Determination of 

 Altitudes," discusses the best method of utilising the readings of aneroid barometers. 

 I hardly think that Mr. WHYMPER makes due allowance for the fact that in 

 mountain ascents the reduction of pressure is very gradual, even at the lower stages. 

 This allows accommodation to take place, so that on arrival at the summit the 

 instrument will not behave as it would have done if rapidly transported there. 

 Again the difference between descending and ascending readings is very different in 

 aneroids whose readings as pressure falls at a given rate may be equally correct, and 

 the difference increases ceteris paribus with the length of time spent on the mountain 

 summit. Thus the advantage to be derived from taking the mean of ascending and 

 descending readings a course which Mr. WHYMPER seems to suggest in some 

 instances is very problematical. 



On his p. 51 Mr. WHYMPER gives an example of a Kew aneroid certificate and 

 then devotes several pages to a criticism of it. On his p. 54 he says, " In the 

 absence of directions to the contrary, it may be assumed by persons into whose 



