86 Me. Pogson on the Madras Celestial Survey. 



than any other event recorded in the annals of the science 

 Numerous atlases and catalogues of stars have been made 

 within the last half century, but until recently, none which 

 could be regarded as faithful and indubitable representa- 

 tions of the heavens at the date of their construction. Ce- 

 lestial charts were formerly made by merely plotting down 

 observed stars from known catalogues, without subsequent 

 telescopic revision. As may be readily imagined, maps so 

 formed abounded with omissions and errors ; stare being 

 frequently inserted of a fainter class than was intended for 

 the limit of magnitude, while numerous brighter ones were 

 left out altogether. The great catalogues, and most espe- 

 cially the zone observations made under the direction of 

 the eminent astroBomers Lalande, Bessel, and Argelander, 

 comprising above one hundred thousand different stars, 

 valuable and accurate as the two latter series especially are, 

 give no definite idea of the stars actually visible with a 

 telescope only two inches in aperture. A survey, worthy 

 of being so called, must be so scrupulously revised, that no 

 single star exceeding its stated limit in brilliancy shall be 

 omitted ; and the fact of an object not being inserted 

 therein, must be proof of its inferiority to such photometric 

 limit at the time the survey was made. Unless such ac- 

 curacy can be ensured, the whole is comparatively of little 

 worth ; but with patience and perseverance the desired 

 result, though confessedly very laborious, is nevertheless 

 attainable. 



Considerations of this nature induced the distinguished 

 Director of the Royal Observatory at Bonn, to survey and 

 map the entire northern hemisphere, including all stars 

 down to the 9 J magnitude, and aided by his well-trained 

 assistants, the enormous task v/as completed in less than 

 eight years. Professor .Argelander and his staff commenced 

 operations in the spring of 1852 and concluded the requisite 



