208 MACLEAR'S REDUCTION OF [Jan. 26, 1857. 



nance maps of all the counties of Ireland, on the scale of six inches 

 to the mile ; together with general maps of Ireland ; Black's Atlas 

 of North America, presented by the publisher ; Atlases of heights, 

 by J. M. Ziegler, Corresp. f.r.g.s. ; with the Transactions of the 

 Darmstadt Geographical Society, of the Hakluyt Society, &c. 



Announcements. — The Sixth Number of the ' Proceedings,' pub- 

 lished that day, would be distributed to the Fellows by Mr. Stan- 

 ford, of 6, Charing Cross. 



The Papers read were : — 



1. Extract frmn a Letter addressed hy Th. Maclear, Esq., H. M. 

 Astronomer at the Capet to the Secretary/ 



" Royal Observatory, Cape of Good Hope, 



Nov. 3, 1856. 



" The object of this letter is to report progress in the reduction of 

 the astronomical observations, which that remarkable and excellent 

 man Dr. Livingston, made for geographical positions, on his track from 

 Loanda across the continent to Quilimane. He has sent them to me 

 for reduction, and I am anxious that they should be in Sir E. Mur- 

 chison's hands, according to Livingston's request, with the least pos- 

 sible delay : or rather, I am anxious that they should meet him in 

 England at the right time — the time when the Society and the public 

 at large, will be doing him due honour for services without a 

 parallel. 



1. To expedite the reductions, I had skeleton forms printed for 

 the computation of ^/me /rom altitudes ; for altitudes /rom ^wie; and 

 for Greenwich time from the lunar distances. 



2. His observed lunar distances were compared (roughly) wilh 

 tabular lunar distances, in order to detect errors of date as to the 

 day of observation — a common source of error where civil clashes 

 with astronomical reckoning. 



3. The watch error was computed from each altitude, whether 

 observed for watch-error or for the calculation of parallax and 

 refraction, to detect errors of entry or of transcribing ; and while 

 this tvas going on, another computer was following closely, cal- 

 culating the parallaxes and altitudes for the times of lunar distance 

 measures. 



The total number of altitudes computed for time is 214, exclusive 

 of repetitions or checks. 



To this point the reductions w^ere brought up on Saturday. To- 

 day we commence the lunar distances, which will be computed by 

 the rigorous trigonometrical process, viz. the final computation; 



