Natural History. 189 



being the fifth time of attendance, and I was much gratified a few 

 hours after with a visit from the boy, attended by his father, the son 

 himself giving me, with a clear voice, the whole of the circumstances 

 stated in the Times newspaper, and, as I am told, copied afterwards 

 into other papers. 



P. S. It may be proper to state, the boy continues well at the 

 present time. 



Orchard-street , Portman-square, June 1 9, 1 823. 



1. The Greenwich Mural Circle. — Feeling a lively interest in any 

 thing connected with the Royal Observatory, we have, with the 

 greatest satisfaction, seen the results of Mr. Pond's inquiry into 

 the state of the Greenwich mural circle: the experiments prove 

 almost to a mathematical certainty, that this splendid instrument is, 

 after twelve years constant use, as free from error, as even its warmest 

 advocates, or the most accomplished observer, could wish. 



2. Mr. Groombridge's Transit Circle. — Whilst admiring the 

 mechanical skill of him who constructed the Greenwich mural 

 circle, we were much concerned to hear, that there were some 

 grounds to suspect the accuracy of another instrument made by the 

 same artist, and generally considered, little inferior to the Greenwich 

 circle itself; we allude to the four-feet meridian transit circle, late the 

 property of Mr. Groombridge. On this gentleman's retiring from the 

 duties of an active observer, the instrument was disposed of, liable 

 however, to an examination on the part of its maker, as to its 

 efficiency or inefficiency; which investigation being conducted by 

 Mr. Troughton, in the presence of Mr. Groombridge, the late Pro- 

 fessor Tralles, and its intended purchaser, gave reason to fear that 

 some alteration in its figure, had been sustained. Accordingly, future 

 and more minute examination was deemed necessary; and, at length, 

 it was resolved, that comparisons of North polar distances taken on 

 the same nights, with it and the Greenwich mural circle should be 

 entered into°; and the results of many weeks' observations proved, that 

 those obtained by Mr. Groombridge with his instrument, were, to use 

 the words of the Astronomer Royal, " as coincident with those pro- 

 cured by the Greenwich mural circle, as those of the Greenwich 

 mural circle were with themselves." Knowing that the reports of 

 the suspected inaccuracy have extended far and wide, we feel it due to 

 Mr. Troughton who constructed the instrument, and to Mr. Groom- 

 brid«e, who used it, to give publicity to the above statement. It 

 is at" present in Blackmail street, and is having eight additional 

 microscopes applied by Mr. Troughton; it will then have six 

 readin«s to each of its divided circles, so that all error of division will 

 probably be annihilated. We hope ere long to see it actively em- 

 ployed. 



