,1867.] 



President's Address. 



171 



whose official reply, printed by the Bombay Government, I extract the 

 following passage :— 



I should certainly recommend that any new magnetic observatory be 

 furnished with magnetic instruments on the pattern of those at Kew. I 

 would propose that an answer of this tenor be given to the Superintendent 

 of the Bombay Observatory, that the Secretary of State for India in 

 Council, having taken the opinion of the Astronomer Eoyal, approves 

 highly of his (the Superintendent's) acting in concert with the Kew Ob- 

 servatory." 



Still, possibly from inadvertence, Mr. Chambers's application for the 

 instruments required to enable him to obey the instruction of " acting iu 

 concert with Kew" yet remains without a reply. In the meantime the 

 cost of the observatory runs on, whilst the very valuable services for mag- 

 netical science, approved and recommended by the Astronomer Royal, 

 and which Mr. Chambers, having been educated at Kew, is singularly 

 qualified to carry into execution, are in abeyance for want of the ne- 

 cessary instrumental means to execute them, the whole cost of which would 

 be under j6400. We may hope that this oversight will shortly be rectified. 



The publication in the last year of the verification and extension of La 

 Caille's Arc of the Meridian in Southern Africa, by Sir Thomas Maclear, 

 Astronomer at the Cape of Good Hope, announces the completion of a na- 

 tional work, pursued unremittingly for above thirty years, and establishing 

 by its result a conclusion too important in its scientific interest to pass with- 

 out recognition by the Royal Society. Our sole knowledge of the figure 

 of the southern hemisphere rests on the arc of the meridian measured by 

 La Caille, and now reraeasured and extended^by Maclear. The original 

 measurement, notwithstanding the well-known ability of the great astro- 

 nomer under whose superintendence it was executed, has not commanded 

 confidence. The degree inferred from it is far too great, and, if accepted, 

 would lead to the conclusion that the dimensions of the two hemispheres 

 are dissimilar. But La Caille's triangles were observed with a quadrant, 

 not with a circle, and were therefore liable to errors of eccentricity and of 

 figure ; while the effects of local attraction, if recognized at all, were very 

 imperfectly appreciated. These considerations induced Maclear, shortly 

 after his appointment to the ('ape Observator}^, to plan the verification 

 which he has now accomplished. Pursuing the still earlier inquiries of 

 Sir George Everest, he succeeded, though with considerable difficulty, in 

 recovering La Caille's terminal stations ; and, aided by the advice and en- 

 couragement of Sir John Herschel (then at the Cape) and of the Astro- 

 nomer Royal, he commenced the work of a remeasurement in 1836. The 

 proceedings were necessarily tedious ; the measurements of the base, of the 

 triangles, and of the zenith distances were repeated to an extent and with 

 precautions unpractised at the earlier period. The zenith distances were 

 observed with the sector with which Bradley discovered the aberration of 

 light and the nutation of the earth's axis, entrusted to Maclear by the Ad- 



