478 Mr. B. Stewart on certain Experiments [June 18^ 



In like manner for small aneroids ^ve have the following result : — ■ 





19 in. 



20 in. 



21 in. 



22 in. 



23 in. 



24 in. 



25 in. 



26 in. 



27 in. 



28 in. 



29 in. 



30 in. 



Eight at 1 9 in. . . 



•00 



•00 



-f-oi 



+ •02 



— •01 



— •01 



— •02 



-•04 



-•07 



— •10 



-*i5 



-•16 



Eight at 23 in. . . 











•00 



+ •01 



•00 



— •02 



-•07 



— 11 



— •12 



-•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- 





1 9 in. 



20 in. 



21 in. 



22 in. 



23 in. 



24 in. 



25 in. 



26 in. 



27 in. 



28 in. 



29 in. 



30 in. 



No. 8. ^ 



Mean correction , . 



•00 



+ •02 



+ •02 



+ •02 



+•03 



•00 



— •01 



-•04 



-•07 



— •11 



— •12 



-•18 



Mean minus first 

 determination . . 



•00 



— •01 



— •01 



-•03 



— •02 



— •02 



— •02 



— ■01 



-•03 



-•03 



— •01 



•00 



In like manner — 





19 in. 



20 in. 



21 in. 



22 in. 



23 in. 



24 in. 



25 in. 



26 in. 



27 in. 



28 in. 



29 in. 



30 in. 



No. 9. 



Mean correction . . 



•00 



+ •04 



+ •04 



+•03 



+ •03 



+ •04 



+ •04 



+ •04 



-|-*02 



— •01 



-•04 



-•C4 



Mean minus first 

 determination . . 



•00 



— •01 



— *02 



-■03 



— •01 



— '02 



— •02 



— •01 



-•03 



— •02 



— •02 



— •02 



"We may learn from these results that if aneroids which have been sub- 

 jected 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 exibit the results obtained in this direction. 



