146 MR. POND ON THE NEW ZENITH TELESCOPE 



of these difficulties ; I only wish to explain the nature of the experiments, the results 

 of which I am no^v about to lay before the Society. 



We have now three distinct methods of determining the place of any star passing 

 the meridian near the zenith. First, by means of the mural circles ; secondly, by 

 the zenith telescope used alternately east and west, as is usually done with similar 

 instruments ; and lastly, by means of a small subsidiary star, as described by me 

 last year in a paper laid before this Society, and which I am inclined to think more 

 exact than any other method. By the following computations it will be seen that 

 the three methods give results nearly identical; and that when the observations with 

 the two circles are numerous and made with sufficient care, a quarter of a second 

 is the greatest error to be apprehended. 



Royal Observatory, March 10, 1835. 



Results of Obset^vations on y Draconis and Bode 170 Draconis. 

 Zenith distance of y Draconis determined by three different methods. 



Zenith distance, 

 First, — Result by 324 observations with the Mural Circles reduced toi ^^^^' 



the latitude of the Zenith Telescope room, the difference between |> 2 1-36 North. 



which and the Circle room being 0"*65 North J 



By Zenith Telescope employed in the unsual manner by alternate ob- "^ 



} 



aper of 

 last year, and which result I prefer to either of the others . 



serrations East and West ; 28 results 



} 



By means of the subsidiary angle as described in my former paper of'. 



Zenith distance of Bode 170 Draconis determined by three different methods. 



Zenith distance, 

 First,— Result by 132 observations with the Mural Circles reduced toT '^•^^• 



the latitude of the Zenith Telescope room, the difference between \ 1 0-45 South: 



which and the Circle room heing 0"-65 North J 



By Zenith Telescope employed in the usual manner by alternate ob- 1 



servations East and West ; 14 results J 



By means of the subsidiary angle as described in my former paper of 1 



last year, and which result I prefer to either of the others J 



1 0-61 



1 0-74 



