472 



DR. C. CHREB, EXPERIMENTS ON ANEROID BAROMETERS 



In accordance with 22 a trifling + correction ought to be applied to the figures 

 for 1896 to allow for its 4 excess of temperature over 1895 and 1897. On the whole, 

 there appears to be satisfactory evidence of a slight secular lowering of reading in the 

 two aneroids, such as would accompany alteration of a true elastic modulus ; but it 

 certainly did not increase to any sensible extent after the end of the first year. 



In pushing the inquiry further in the case of aneroid No. 4, I took the 25 

 experiments already dealt with in Table XIX., but divided them into an earlier and 

 a later half, treating experiments Nos. 16 and 17 as but one. The results appear in 

 Table XXVII. 



TABLE XXVII. Mean Corrected Errors in Aneroid No. 4. 



At the higher pressures the apparent difference between the earlier and later 

 series is microscopic ; at the lower pressures the figures would point to a secular rise 

 in the corrected errors ; but, as there is no visible tendency in this to increase at the 

 very lowest pressures, its true character is somewhat doubtful. Probably the only 

 safe conclusion to be drawn is that if any real change occurred in aneroid No. 4 it 

 certainly was very small. 



29. For investigating possible secular change in the differences of the descending 

 and ascending readings, the data are somewhat limited, because few of the later 

 experiments were altogether of the normal type. The most suitable data are 

 utilised in Table XXVIII. , which gives the sums of the differences of the descending 

 and ascending readings in experiments of the normal type separated by appreciable 

 intervals of time. When two experiments are combined, the mean sum is taken to 

 the nearest '01 of an inch. 



