347 



how nearly they agree in settled weather, showing that the 

 effect of the two hygrometric corrections is equal and oppo- 

 site. 



From the preceding observations, it appears that on wet 

 days the barometric formula (II.), corrected statically for the 

 hygrometer, gives too great a value for the height. As this 

 fact does not appear to have attracted the attention of ob- 

 servers, it may be useful to confirm it by other cases which 

 have been observed. 



In the following observation of the height of Douce and 

 Sugar Loaf, the lower station was at Kilmacanoge cross roads, 

 at a point marked on the Ordnance Map as 255 feet, or 42 5 

 fathoms. Simultaneous observations were made with a New- 

 man's barometer, which had been carefully compared with my 

 own. 



The lower station at Howth was the foot of the cliff in 

 Balscaddan Bay: — 



Table IV. 



1. Douce, . . 



2. SugarLoaf, 



3. Howth, . . 



Lower Station. 



Upper Station. 



P I / t \ P' /' \f 

 29-663 0-372 58 27-421 0-36150 



29-635 0-37258 28-1530-27851 

 29-684 0-440 63,29- 103 0-419 58 



Ther Hygr. 

 Coeff.l Coeff. 



1-044:1-014 



10451-011 

 1-0581-915 



Observations. 



Aug.31, 1849; wet 

 and foggy at sum- 

 mit of Douce. 

 Aug. 31 ,1849; va- 

 riable. 

 June 28, 1852; 

 wet day. 



In order to compare the heights calculated from these ob- 

 servations with the trigonometric heights of the Ordnance 

 Survey, we must add 42-5 fathoms for the height of the lower 

 station in Nos. 1 and 2, and two fathoms for the height of the 

 lower station in No. 3 above low water of spring tides. These 

 corrections have been made in the followingTable, in which V. 

 denotes the trigonometric heights: — 



