1868.] on Aneroid Barometers. 479 



Table IV. 





ISt hiX. 



8. 



1st Ex. 

 9- 



2nd Ex. 

 8. 



2ndEx. 

 9- 



10. 



II. 



12. 



13- 



14. 



10. 



Correction betore 























experiment .... 



— '10 



— '12 



-•13 



-•09 



— '12 



— •II 



-'13 



-•47 



-•04 



-•05 



Immediately after 























experiment .... 



•00 



+ •03 



+ 'o6 



+ •07 



-r 00 



-■03 



"GO 



-•19 



+ 00 



-f--o4 



1 8 hours after ex- 

























-•07 



-•03 



+•04 



4- "02 





— •10 



-•07 



-•34 



4-01 



4--OI 



4-8 hours after ex- 























-•08 



-•04 







-•03 







-■37 







3 days after ex- 

























-•08 



-•05 















— •01 



— •01 



3 weeks after ex- 

























-•13 



— •10 







— •II 









-•07 



-•06 



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 

 he some considerable time before it recovers its previous 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 analogous to ascents 

 in a balloon, or descents from a mountain ; they are not, however, pre- 

 cisely 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 intervals of 

 30 minutes, the aneroids being well tapped. 



The following corrections were obtained for down readings (instruments 

 supposed right at 30 inches). 



Table V. 



At 



No. 8. 



No. 9. 



At 



No. 8. 



No. 9. 



inches. 







inches. 







30 



•00 



•00 



23-5 



4-^o8 



— •02 



29-5 



•00 



- 03 



23 



4--II 



-•03 



29 



•00 



-•04 



22*5 



4--I2 



— •01 



28-5 



•00 



-•03 



22 



+•14 



•QO 



28 



•00 



-•03 



21-5 



+•16 



+ •02 



27-5 



•CO 



— •02 



21 



+•17 



4--04 



27 







20*5 



4-*2o 



+ •06 



26-5 



•00 



— •02 



20 



4-'22 



+•07 



26 



4- -CI 



— -02 



19-5 



+•25 



4-*09 



25-5 



4- -04 



— •02 



19 



+•27 



+ •11 



25 



+ •05 



-•04 









24-5 



+ •06 



— •02 









24 



+ •05 



— •01 









