484 DR. C. CHEEE, EXPERIMENTS ON ANEROID BAROMETERS 



We should conclude from the table that an hour's stoppage at 21 inches lowered 

 the creep during the subsequent stoppage at 15 inches by only 4 per cent. An hour's 

 stoppage at 18 inches was distinctly more effective, but still not very serious. 

 Stoppage for 26 hours had a much larger influence, reducing the creep at 15 inches 

 from 100 to 74 when it occurred at 21 inches, from 100 to 38 when it occurred at 

 18 inches, and from 100 to 13 when it occurred at 16 inches. 



According to the table : 



Influence of an hour's stoppage at 21 _ _ jt 



Influence of an hour's stoppage at 18 10 



Influence of 26 hours' stoppage at 21 26 



"T^T T~ 4^. 



Influence of 26 hours' stoppage at 18 62 



This suggests that the influence of a stoppage on the creep at a lower stationary 

 pressure may be expressible as a product of two factors, one a function of pressure 

 only, the other having for sole variable the duration of the subsidiary pressure. 



Again, taking the three experiments when the subsidiary stoppage lasted 26 hours, 

 it will be noticed that the mean ratios, "13, '38, and 74, are to one another nearly in 

 the proportion 1:3:6, which corresponds to the pressure intervals 16 to 15, 18 to 15, 

 and 21 to. 15 inches. 



Whether we have to do here with chance coincidences or with physical laws it 

 would be impossible to say without further somewhat elaborate experiments. 



37. Before leaving Table XXXVIII. we may note its bearing on the laws 

 established in 16 to 19 for change of reading under steady pressure. The data 

 deduced from the subsidiary stoppages at 21 and 18 inches, and the stoppages at 

 15 inches in the three standard experiments, are in good agreement with the laws 

 that the fall of reading in a given time during a stoppage, preceded by a reduction 

 of pressure at a uniform rate, is proportional to the pressure range, and that the 

 mode of variation of the reading with the time is independent of the range. The 

 first of these laws is supported by the closeness of the " mean " and " theoretical " 

 ratios, the second by the absence of any clear tendency in the ratios of the falls at 

 the specified intervals to either increase or decease as the intervals become longer. 



Further support of the first law is supplied by the fact that the mean observed 

 falls during 26 hours' exposure to the pressures of 21, 18, and 16 inches were respec- 

 tively '13, '193, and '226 inch, and we have 



13/9 = 'Ol'l, -193/12 = '0161, -226/14 = '0162, 



values nearly equal. 



A very interesting point is that the ratios borne by the falls at 15 inches pressure, 

 in the several experiments where a subsidiary stoppage existed, to the corresponding 

 falls in the standard experiments are, to all appearance, constant throughout the 

 hour's stoppage at 15. There are, of course, irregularities in the figures, but there 



