482 DR. C. CHRBB, EXPERIMENTS ON ANEROID BAROMETERS 



and this is greater than in experiments 63 and 66 by 



075 '03, or '045 inch. 



Thus an hour's stoppage at 18 diminished the total creep between 18 and 15 by 

 045 inches. 



These examples should suffice to explain Table XXXVII. 



TABLE XXXVII. 



35. In arguing from a limited number of experiments allowance must be made for 

 accidental coincidences. The general conclusions to be drawn from Table XXXVII. 

 seem however prett} r obvious.' 5 " A stoppage has two effects, tending somewhat to 

 neutralise one another. It lowers the reading, but while doing so it diminishes the 

 tendency to further creep as pressure is further lowered. For instance, stoppage for 

 2G hours at 18 inches lowered the reading at 18 inches in aneroid No. 4 by '18 inch, 

 but lessened the subsequent creep between 18 and 15 inches by '06 inch. Conse- 

 quently on arrival at 15 inches the aneroid read only '12 inch lower than if there 

 had been no stoppage at 18 inches. When the stoppage occurred at 21 inches, and 

 lasted only an hour, the diminution in the creep between 21 and 15 inches nearly 

 obliterated all influence on the reading at 15 inches. With increased duration of 

 stoppage the direct lowering of reading tended more distinctly to predominate. 



The lower the pressure at which stoppage occurs, the greater influence does it 

 exert in both directions. To realise this one should notice that stoppage at 21 inches 

 influenced the creep over the 6 inches 21 to 15, whereas stoppage at 16 inches 

 influenced the creep over a single inch only. 



36. The way in which the influence of a stoppage tends to disappear the further 

 the pressure is lowered below the stationary point, is brought out most clearly by a 

 consideration of the phenomena observed after the lowest pressure is attained. 



In treating of this I have utilised, in addition to experiments Nps. 62 to 70, two 



* At the same time, so far as concerns phenomena occurring daring actual change of pressure, it 

 would be difficult to distinguish between a temporary rise in true elastic moduli and a diminished 

 tendency to creep. 



