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XXXIY. 



ON THE POSITION OF ENCKE'S COMET AS DEDUCED 

 EROM PHOTOGEAPHS TAKEN BY MR. W. E. WILSON. 

 By ARTHUR A. RAMBAUT, D.Sc, E.R.A.S. 



[Read Februaky 11, 1893]. 



Two photographs taken by Mr. W. E. Wilson on the night of 

 November 30th, 1894, show Encke's Comet and the stars in its 

 neighbourhood, each plate being given an exposure of 30 minutes in 

 his two-foot reflecting telescope. 



As observations of this comet, at such a distance as it then was 

 from the sun, are quite out of the reach of any telescopes of moderate 

 dimensions on account of the faintness of the object, I was much 

 pleased when I learned that these photographs had been secured, and 

 immediately requested and obtained his permission to measure the 

 plates, with the view of obtaining the position of the comet. 



The plates were measured in the micrometer-microscope at the 

 Dunsink Observatory, which belongs to the Royal Irish Academy. 

 This was done in very much the manner described in a Memoir by 

 Sir Robert Ball and myself, which was read before the Academy on 

 April 25, 1892, and published in Vol. xxx.. Part iv., of its Trans- 

 actions. 



As there was, however, only one exposure on each plate in this 

 case, and in the method elaborated in that Memoir two exposures 

 between which the telescope had been displaced in right ascension 

 were contemplated, a slightly diflFerent procedure from that recom- 

 mended therein had to be pursued. 



In the neighbourhood of the comet I found photographs of two 

 stars of the Bonn Durchmustering, namely, + 7°, 4886 and 4887. 

 The first of these was at such a small distance from the centre of the 

 plate that no sensible error could be introduced by taking it as the 

 origin of rectangular co-ordinates, as is shown by an application of 

 the formulse on p. 241 of the Memoir referred to above. 



If a, S, are the right ascension and declination of the star from 



