AT KEW OBSERVATORY AND THEIR DISCUSSION. 



495 



In the other 27 aneroids the creep in the first day bore to that in the first week a 

 ratio lying between '6 and '9. It is also not unreasonable to suppose that some at 

 least of the extreme values were appreciably influenced by permanent changes of zero. 



50. Notwithstanding the absence of information as to the exact nature of the 

 operations, Mr. WHYMPER'S experiments are of much interest, inasmuch as they 

 supply information of an almost unique kind relative to the effects of very prolonged 

 exposure to low pressures. I have thus examined the results with considerable care, 

 with a view to seeing what light they throw on the phenomena already described. 



There are, in the first place, several tables whose contents afford the opportunity 

 of determining how far it is possible to represent the creep over a series of weeks 

 at a low pressure by a single algebraic term Cf, as in (7), 18. 



Thus, on his p. 17 Mr. WHYMPER gives the errors, relative to a mercury 

 barometer, in six aneroids exposed together for six weeks to a pressure of 22| inches. 

 Readings were taken at the end of each week. How exactly equal the " weeks " 

 were is not stated ; but a few hours' variability in such a case would hardly matter. 

 At the end of four weeks the readings had become, if not absolutely stationary, so 

 nearly so that the probable error of reading began to be too serious. 



In Table XLV. I give the ratios I find borne to the first week's creep by the total 

 creeps up to the end of the second, third, and fourth weeks; also the values found 

 for q in the algebraic term by taking separately the mean values of the above 

 three ratios. 



TABLE XLV. Creep Eatios, calculated from data on Mr. WHYMPER'S p. 17. 



The irregularities apparent in the data for some of the aneroids are not surprising, 

 in view of the fact that the average creep recorded in the fourth week was only 

 "013 of an inch. 



The mean results agree well with the single term formula (7). 



The next set of data I have utilised are given on Mr. WHYMPER'S p. 19. They 

 refer to three aneroids distinct from those of Table XLV. exposed for eight weeks 

 to the pressure of 16 inches. In these the increase of creep can be fairly traced up 

 to the end of the sixth week. The individual aneroids show somewhat irregular 

 behaviour. I give the mean results, obtained in the same way as the corresponding 

 results in our last table. " Iw " stands for " one week's creep, ' and so on. 



