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tages attendant on the building in which he was compelled to reside, 

 rendered it impossible that he should retain the situation. Accord- 

 ingly, in a letter, dated May 27. 1833, he tendered his resignation 

 to the Lords of the Admiralty, adding that, on his return to Eng- 

 land, he would immediately proceed to the task of calculating and 

 reducing the various observations he had made, and of extracting from 

 them those useful results they were intended to afford. 



Amongst the other annoyances to which Mr Henderson was subject 

 at the Cape, may be mentioned that, which had been the source of much 

 vexation to his predecessor, the state of the mural circle. Mr 

 Fallows had found remarkable anomalies amongst the readings of the 

 several microscopes, in different positions of the instrument, during 

 a revolution upon its axis ; whence he had been led to infer that it 

 had suffered a change of figure since leaving the maker's hands. Mr 

 Henderson's first employment was the rigid investigation of these 

 anomalies, the results of which are printed in the eighth volume of 

 the Memoirs of the Astronomical Society, p. 141. He came to the 

 conclusion, that the anomalies proceeded partly from an oval foi-m 

 which the instrument had acquired, and partly from variations in 

 the position of the centre of the instrument while revolving, relative 

 to the microscopes, owing probably to the pivots not being exactly 

 circular ; whilst, in addition, the whole instrument frequently 

 changed its position upon the pier, from the Y support of the front 

 pivot not being perfectly steady. He agreed, moreover, with Mr 

 Fallows in concluding, that the mean of the readings of six micro- 

 scopes is little, if at all, affected by these causes ; so that, on the 

 whole, it appeared that the degree of accuracy to be obtained from 

 the instrument was not inferior to that given by the best instruments 

 of similar construction hitherto made. The conclusion of the mat- 

 ter is this : — on the circle being brought to this country and ex- 

 amined by Mr Simms, it was found that the large steel collar car- 

 ried by the conical axis was quite loose ; — " a child's hand could 

 turn it." 



On Mr Henderson''s return to Edinburgh he set about reducing his 

 own observations ; a task voluntarily imposed on himself, and one 

 which he sacrificed his own interests to fulfil. No long period elapsed, 

 however, before a situation opened, in every way suited to his taste. 

 An agreement was entered into between the Commissioners of the 

 Treasury and the members of the Astronomical Institution of this 

 place, whereby the latter gave their observatory and instruments to 

 the use of the Professor of Practical Astronomy in the University, 



