328 



this region of the sky, which is invisible in Eu- 

 rope. The stars near the south pole are ob- 

 served in general with so little perseverance 

 and assiduity, that the greatest changes may 

 take place in the intensity of their light, and 

 their own motion, without astronomers having 

 the slightest knowledge of them. I think I 

 have remarked changes of this kind in the con- 

 stellation of the Crane, and in that of the Ship 

 Argo. I compared at first with the naked eye 

 the stars which are not very distant from each 

 other, in order to class them according to the 

 method pointed out by Mr. Herschell % in a 

 paper read to the Royal Society of London in 

 1796. I afterwards employed diaphragms di- 

 minishing the aperture of the telescope, and 

 coloured and colourless glasses placed before 

 the eye-glass ; and more particularly an instru- 

 ment of reflexion calculated to bring at the 

 same time two stars into the field of the tele- 

 scope, after having equalized their light by re- 

 ceiving it with more or fewer rays at pleasure, 

 reflected by the quicksilvered part of the mirror. 

 I admit, that all these photometric processes 

 are not of great precision ; but I believe, that 

 the last, which perhaps had never before been 



* Phil. Trans, for 1796, p. 166. (Compare also Pigotfc 

 and Goodrich in the Trans., vol. Ixxv,, Part 1, p. 127, 154, 

 and vol. lxxvi, Part 1, p. 197.) 



