no Report S.A.A. Advancement of Science. 



(b) St. Helena, 1840-1847, 

 Long. oh. 22m. 41.9s. W. of Greenwich or 



,, ih. 2m. 28.4s. W. of Gottingen. 

 Lat. —15° 56° 41.2' S. 



Height of barometer cistern above mean sea-level 1764-5 

 feet (by levelling). 



The observations considered extend from 1840 May to 1847 July, 

 with one interruption. They are published in detail in Sabine's 

 " Observations made at the Mag. and Met. Observatory at St. 

 Helena." Vols. L and II. London, 1847-1860. The barometer 

 was made by Newman according to a description given by the Royal 

 Society. The internal diameter of the tube is o.6ins. The scale 

 terminating in an ivory point, is movable. The barometer would thus 

 appear to be of the same type as that which is still in use at the Cape 

 Observatory, but the latter has an internal diameter o.iin. less. Until 

 Sept., 1842, observations were taken at every even hour of Gottingen 

 mean time, after that date until the conclusion of the series, at every 

 hour. Observations were intermitted for 24 hours on Sundays and 

 holidays. The barometer was moved in August, 1840, to a position 

 19 feet higher. The height given above is that of the barometer after 

 removal. The observations of 1840, May- July, are reduced to 1764-5 

 feet. 



Before leaving England, the barometer was compared with the 

 Royal Society's Standard, and found to require a correction of 

 - o.oo7ins. This correction includes the thermometer error. It was 

 intended to make another comparison with the Standard after the 

 conclusion of the observation, but no record of this having been done, 

 has been found. In 1844, from 22nd April to 3rd May, simultaneous 

 observations were made with another barometer near sea-level. The 

 mean difference between the two barometers when corrected for all 

 known errors, was found to be i.786ins., which must be increased by 

 0.009 for reduction to sea-level, the lower barometer being 9.3 feet 

 above sea- level. 



Table i gives the mean monthly readings of the barometer at the 

 above station reduced to 32° F. and Lat. 45°. No correction for 

 decrease of gravity due to altitude has been applied, — this has not 

 been necessary, as it is naturally included in the comparison with the 

 barometer near sea-level. 



The extreme readings of the barometer in each season (reduced as 

 in Table i) are : — 



Season Highest Lowest Range 



ins. 



1840-41 28.388 on 24 July, 



41-42 .388 on 9 June, 



42-43 .440 on 9 July, 



43.44 .408 on 27 Aug, 



44-45 .426 on 15 July, 



45-46 .391 on 13 J"b^ 

 46-47 -405 on 17 July, '46 



