﻿Ml*. B. Stewart on certain Experiments on Aneroid Barometers. 73 



Table IV. 



ist Ex. 



i st Ex. 

 9- 



2nd Ex. 

 8. 



2ndEx. 

 9- 



10. 



11. 



12. 



-•13 --o 9 



-•12 



— •11 



-'*3 



+ •06 +-07 



+ •06 



-•03 



•00 



+ •04 , +-02 





— •10 



-•07 



.. 





-•03 











— •11 







13- 



14. 



16. 



-•47 



-•04 



-•05 



-•19 



+ •06 



+ •04 



-*34 



+ •01 



+ •01 



-'37 









— ■01 



— •01 





-•07 



— "c6 



Correction before 

 experiment .... 



Immediately after 

 experiment .... 



18 hours after ex- 

 periment 



48 hours after ex- 

 periment 



3 days after ex- 

 periment 



3 weeks after ex- 

 periment 



•10 



-co 

 ■•07 

 -•08 

 -•08 



•13 



— •12 



+•03 



-*°3 

 -•04 

 -•05 



— •10 



It thus appears that if an instrument reads correctly before it is 

 put into the receiver it will read too low immediately afterwards, 

 and that it may be some considerable time before it recovers its pre- 

 vious reading. The instrument cannot, therefore, be safely trusted 

 for absolute determinations if it has been recently exposed to rapid 

 changes of pressure. 



The experiments hitherto recorded, in which an inch of pressure 

 has been taken away or added every ten minutes, are perhaps analo- 

 gous to ascents in a balloon, or descents from a mountain ; they are 

 not, however, precisely analogous to mountain-ascents, since a longer 

 time than 1 minutes is usually taken to produce a change of pressure 

 equal to 1 inch. 



At the suggestion of Mr. Charles Brooke, a couple of aneroids 

 were tested in April 1868, with the view of rendering the experiment 

 more analogous to a mountain-ascent. 



The pressure was reduced by half an inch at a time and at inter- 

 vals of 30 minutes, the aneroids being well tapped. 



The following corrections were obtained for down readings (instru- 

 ments supposed right at 30 inches). 



Table V. 



At 



Mo. 8. 



No. 9. 



At 



No. 8. 



No. 9. 



inches. 







inches. 







30 



•co 



•co 



23'5 



+•08 



— '02 



29"5 



•00 



- °3 



23 



+ •11 



-•°3 



29 



•00 



-•04 



22*5 



4--I2 



— •01 



28-5 



•00 



-•03 



22 



+•14 



•00 



28 



•00 



-•03 



21-5 



4-16 



4- - 02 



27-5 



"CO 



-•02 



21 



+ •17 



+•04 



27 







20-5 



4- '20 



+•06 



26*5 



•00 



— •02 



20 



+ •22 



+•07 



26 



+•01 



— •02 



I9-5 



+ •25 



+•09 



25'5 



4- -04 



— •02 



J 9 



+ •27 



4-"ii 



25 



+ •05 



-■04 









24-5 



4-'o6 



— •02 









24 



4- -05 



— Ol 









