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III. Observation of the Summer Solstice, iSiQ, at the Royal Ob" 

 servatory. By John Pond, Esq. Astronomer Royal, F. R, S, 



Read November 12, 1812. 



As it is intended that a minute description of the mural 

 circle lately erected at the Royal Observatory, when com- 

 pletely finished, shall be laid before the Royal Society, I think it 

 unnecessary to accompany this communication with any other 

 remarks on its construction, than such as are absolutely neces- 

 sary to render the annexed observations intelligible; being 

 only anxious to take an early opportunity of transmitting the 

 result of the observations of the sun, made at the last summer 

 solstice. For, notwithstanding the instrument was at that 

 time in a very unfinished and imperfect state, I have rea- 

 son to think, that the observations made with it were much 

 more exact than could have been made with any other instru- 

 ment hitherto constructed ; the uncertainty of the result, as 

 far as the instrument itself is concerned, does not, I believe, 

 exceed a small fraction of a second ; but I think it necessary 

 to offer a few remarks on the elements of the computation, 

 by which the result is obtained. 



The distance of the sun from the pole at the moment of the 

 solstice, may either be considered as a simple arc, or as com- 

 posed of two others, namely, the distance of the sun from the 

 zenith, and the distance of the zenith from the pole. From 

 the construction of instruments which take their point of de- 

 parture from the position of a plumb-line or level, it is a general 



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