Introduction. 



xlvii 



METEOROLOGICAL INSTRUMENTS. 



§ 8. Barometer. 



55. A Mountain Barometer, by Adie & Son, was used from July 1841 till 

 January 1842. The scale is engraved on the brass tube, and reads, with a vernier, 

 to 0.002 in. ; the mercury in the limb of the cistern is adjusted at each observation 

 to a constant zero point ; the tube is about 0.15 inch diameter. 



56. After January 1. 1842, a Standard Barometer, by Newman, was placed in 

 the Observatory. The diameter of the boiled tube is 0.552 in. ; the scale is attached 

 to a brass rod, terminating in an ivory point, which, at each observation, is made to 

 meet its image in the mercury of the cistern. The vernier professes to read to 

 0-002 in., and O'OOl may be estimated ; but the graduation is so inexact, as to give 

 changes in error from 0-002 to 0*003 in. 



The barometer by Newman was compared indirectly with the standard of the 

 Royal Society, London, by means of one belonging to the Duke of Argyle. The 

 comparisons were made in London. 



Table 23. — Comparisons of the Duke of Argyle's Standard Barometer with the Standard 



Barometer of the Royal Society of London. 



Royal Society's Standard. 



Duke of Argyle's Standard. 



Error 



of Duke of 



Argyle's 



Standard. 



Flint Glass. 



Crown Glass. 



Tempera- 

 ture. 



Height. 



Tempera- 

 ture. 



Corrected to Tem- 

 perature of R. S. 

 Standard. 



in. 



29-280 

 29-490 

 29-462 

 29-252 

 29-366 

 29-210 



in. 



29-274 

 29-482 

 29-454 

 29-246 

 29358 

 29-204 



36-9 

 39-0 

 40-0 

 41-6 

 41-3 

 43-2 



29-302 

 29-496 

 29-460 

 29-256 

 29-372 

 29-214 



37-2 

 39-0 

 40-6 

 42-0 

 42-0 

 43-5 



in. 



29-301 

 29-496 

 29-458 

 29-255 

 29-370 

 29-213 



in. 



+ 0024 

 + 0-010 

 + 0-000 

 + 0-006 

 + 0-008 

 + 0-006 



The mean correction of the Duke of Argyle's Barometer to the Royal Society's 



in. 



is -0.009. 



