.1868.] 



on Aneroid Barometen 



477 



jectecl to a decrease of pressure similar to that to which they were subjected 

 in these experiments — 



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

 to 24 inches, but after that pressure its reading will be considerably lower 

 than that of a standard barometer, so that a large positive correction will 

 have to be applied. 



(2) That small aneroids are less trustworthy than large ones, and pro- 

 bably cannot be trusted below 26 inches. 



(3) That if previous experiments are made upon an aneroid, we are 

 enabled by this means to obtain a table of corrections which, when applied 

 to future observations with the same instrument, will most probably pre- 

 sent us with a much better result than had we not verified our instrument 

 at all, and that by this means we may use our instrument dov^n to 1 9 

 inches with very good results. 



Let us now consider the up readings of these instruments, and let us 

 suppose that each instrument is right to begin with, that is to say, while 

 remaining an hour and a half at its lowest reading. 



These corrections and up readings are exhibited in the following 

 Table :— 



Table III. 



No. of 

 ane- 

 roid. 



Correction for the up readings of the aneroids of Table I. supposed right 

 with standard at lowest reading. 





19. 



20. 



21. 



22. 





24. 



25- 



26. 



27. 



28. 



29. 



30. 



8. 



•00 



+ •03 



+ •03 



+ •05 



+ •05 



-|-'02 



+ •01 



-•03 



-•04 



-•08 



— •II 



-•18 



9- 



•00 



+ •05 



+ •06 



+ •06 



+ •04 



+ •06 



+ •06 



+ •05 



+ •05 



+ •01 



— •02 



— •02 



8. 



•00 



+ •02 



+ •01 



•00 



+ *02 



— •01 



-•03 



-•06 



— •II 



-•15 



-•16 



-•19 



9- 



•00 



+ •03 



+ •03 



— •01 



-I--01 



+ •02 



+ •02 



+ •04 



•00 



-•03 



-•06 



-•06 



lO. 



•00 



•00 



+ •03 



+ •04 



+ ■03 



+ •07 



+ •05 



+ •02 



•00 



-•05 



-•08 



— •I I 



II. 



•00 



-•04 



— •02 



•00 



-•03 



-•05 



-•08 



— •11 



-•14 



-•13 



-•16 



-•14 



12. 



•00 



+ •01 



— •02 



— •02 



— •I I 



-•12 



— •12 



-•14 



— •21 



— •20 



-•24 



-•26 





•00 



+ •05 



+ •05 



+ •06 



+ •05 



+ •05 



+ •05 



+ •05 



+ •05 



— 'OI 



— •II 



-■14 



14. 











•00 



+ •09 



+ •12 



+ •12 



+ •11 



+ •07 



+ •03 



+ •02 













•00 



— 'OI 



-•06 



-•06 



-•08 



-•09 



-•06 



-•08 



16. 











•00 



+ •02 



+ •03 



•00 



-•03 



-•04 



-•07 



-•06 













•00 



+ •01 



— •02 



-•04 



— •II 



-•19 



-•28 



-'33 



Hence we find the mean up correction for large aneroids : — 





19 in. 



20 in. 



21 in. 



22 in. 



23 in. 



24 in. 



25 in. 



26 in. 



27 in. 



28 in. 



29 in. 



30 in. 



Supposed right at 



•00 



+ •03 



+ •03 



+•03 



+ ■03 



■+••02 



+ •01 



•00 



-•03 



-•06 



-•08 



— •II 





Supposed right at 

 23 in 











•00 



+•04 



+•03 



+ •03 



+ •01 



— •01 



— •02 



-•03 



