339 



ively two hours before and two hours after the same hours of 6 and 

 18. The extreme inequahty, or the amount of lunar variation 

 measured from one extreme elongation to the other, is about 28" of 

 arc at Toronto, 20" at Hobarton, and 11" at St. Helena. The 

 resolved portion of the terrestrial magnetic force which acts in the 

 horizontal direction, and is opposed to any disturbing influence, is 

 approximately 3*54 at Toronto, 4'51 at Hobarton, and 5-57 at St. 

 Helena. 



November 24, 1853. 

 The EARL OF ROSSE, President, in the Chair. 

 The Earl of Harrowby was elected. 

 Captain Inglefield, R.N., was admitted into the Society. 

 The following gentlemen were elected Auditors of the Treasurer's 

 Accounts on the part of the Society: — Capt. FitzRoy, Mr. Grove, 

 Mr. Phillips, The Rev. Baden Powell, Mr. Wheatstone. 



The following extract of a letter from Lieut. Gilliss, U.S.N, to 

 Colonel Sabine, R.A., was read: — 



Washington, 12 Sept. 1853. 



Lieut. Mackai returned to the United States in April, having made 

 his magnetical observations successfully at all the elevations and at 

 distances of 100 miles, entirely across the Pampas. Soon after leaving 

 Mendoza he was thrown from his horse, breaking his barometer and 

 so injuring his chronometer, that he has neither the longitudes of 

 his magnetical stations nor barometric profile of the country. Being 

 desirous to make his work complete, he volunteered to retrace his 

 ground, and left the United States for the purpose more than a month 

 ago, taking with him the declinometer and dip-circle, two Bunten's 

 barometers, an apparatus for determining altitudes from the boiling- 

 point, and some smaller instruments. 



Conveyance of the unifilar would have required another mule. 



Cursory inspection of the observations already made afforded evi- 

 dence of their reliability, and as repetition would have involved 

 many hours' detention at each station, it was not considered essen- 

 tial to cumber him. Should the Argentine provinces have become 

 sufficiently quiet, he will first cross the Andes at the Planchan Pass, 

 lat. 35° 20', next at the Partillo (the most elevated) Pass, lat. 33° 40', 

 and finally at the Cumbre and Uspalata Pass, in lat. 32° 50', where 

 observations have already been made. 



As he will remain at Santiago only a short time, I look for him 

 home during February next. 



His and all the magnetical observations will then be discussed, 

 and the volume be ready for press by the close of 1854. Those on 

 meteorology are very far advanced. 



The astronomical observations will fill three volumes, one of which 

 (Mars and Venus) will be ready about the same time as the mag- 

 netical and meterological volume ; the zones not until two years 

 later. 



24* 



