﻿72 Royal Society : — 



In like manner for small aneroids we have the following result : 



19 in. 



20 in. 



21 in. 



22 in. 



23 in- 



24 m. 



25 in. 



— •02 



"CO 



26 in. 



-•04 

 — •02 



27 m. 



-•07 

 -•07 



28 in. 



29 in. 



30 in. 



1 



Eight at 19 in. . . 



Eight at 23 in. . ■ 

 I 



•00 



•00 



+ •01 



+ •02 



— •01 



•00 



— *OI 



-foi 



— •10 



— 11 



- -I 5 

 — •12 



-•16 

 -19 



As before, there are two instances in which the same instrument was 

 twice tried ; assuming the mean of the two trials to represent the truth, we 

 find— 





19 m. 



20 in. 



21 in. 



22 m. 



23 in. 



24 in. 



25 m. 



26 in. 







27 in. 



28 m. 



29 m. 



30 m. 



No. 8. 











Mean correction . . 



•00 



+ •02 



+ •02 



+ •02 



+ •03 



-co 



— ■01 



-•04 



-•07 



— •1 1 



— •12 



-•18 



Mean minus first 



























determination . . 



•00 



— •01 



— •01 



— •03 — -02 



| 



— •02 



— •02 



— •01 



-•°3 



-•03 



— •01 



•00 



In like manner- 





19111. 



20 in. 



21 in. 



22 in. 

 +•03 

 -'°3 



23 m. 



24 in. 



25 m. 



26 m. 



27 in. 



28 in. 



29 in. 



30 in. 



No. 9. 

 Mean correction . . 



Mean minus first 

 determination . . 



-co 

 •00 



4- -04 

 — •01 



+ •04 

 — •02 



+ •03 



- 



+ •04 

 — •02 



+ •04 

 — •02 



+ •04 

 — •01 



-{-'02 



-•°3 



— •01 

 --"02 



-•04 

 — •02 



-•c 4 

 — •02 



We may learn from these results, if aneroids which have been 

 subjected for at least one hour and a half to the lowest pressures 

 which they register have the pressure increased by means of the 

 gradual introduction of air into the receiver (after the manner already 

 described) : — 



(1) That a well-constructed large aneroid will not go far wrong for 

 about 8 inches above the lowest pressure. 



(2) That in this respect small aneroids are somewhat less trust- 

 worthy than large ones. 



(3) That if the instrument read be previously tested and its cor- 

 rections ascertained, we may consider it trustworthy (making use of 

 these corrections) for up readings throughout a greater range than 

 if it had not been so tested. 



I come now to consider whether a rapid change of pressure affects 

 an aneroid after the experiment has been completed. 



The following Table will exhibit the results obtained in this direc- 

 tion : — 



