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On the Powers and Use ofKater's Altitude and Azimuth Circle, 

 By Mr W. Galbraith. 



The importance of a small portable astronomical instrument, 

 for the purpose of enabling scientific travellers to determine 

 readily latitudes and time with sufficient precision to regulate 

 chronometers, and thereby to find their longitude, has been long 

 felt, and several expedients have been resorted to for the accom- 

 plishment of this end with various success. The small pocket 

 sextant with an artificial horizon has been long used with con- 

 siderable advantage. An instrument of this kind was generally 

 employed by the celebrated traveller Mungo Park, on which 

 several papers have been written, and the results of his obser- 

 vations form the subject of a memoir by M. D'Avezac, entitled, 

 Examen et rectification des positions determinees astronomique- 

 ment en Afrique par Mungo ParTa. This was read to the Aca- 

 demy of Sciences at Paris on the 19th of August 1833, and of 

 which an account is given in the Con?iaisance des Terns pour 

 1836. 



The inconvenience attending the carriage and use of a mer- 

 curial horizon has been often complained of, and this induced 

 the late Captain Kater to contrive a small altitude and azimuth 

 circle, to be rectified by a spirit level permanently fixed to the 

 instrument, which seems to answer the purpose admirably. The 

 first of the kind the writer of these remarks had an opportunity 

 of seeing, was one belonging to Captain Basil Hall, and made by 

 T. C. Robinson, optician, Devonshire Street, Portland Place, 

 London. The observations made with it were susceptible of 

 very considerable precision, notwithstanding its moderate di- 

 mensions, the circles being, I believe, only about three inches in 

 diameter. 



" With respect to my little circle," says Captain Kater, in a 

 letter to me of the 31st of June 1834, " there is no description 

 of it published, and the state of my health is such, that I can- 

 not undertake to do it, though I am convinced it is much 

 wanted. My object in its construction was perfect portability 

 and facility in its use, joined to a degree of accuracy sufficient 

 for all the purposes of a scientific traveller. I therefore limited 

 its diameter to three inches, and the reading to one minute. 



