Meteorological and Astronomical Notices. 385 



tity of rays for measurement, he takes a smaller and smaller 

 part of them. With a star of the sixth magnitude the aper- 

 ture is only 015 inch, or less than the pupil of the eye, and 

 therefore at once throwing away all the power, were it em- 

 ployed, of even a Rosse's gigantic reflector. With a star of 

 the second magnitude the aperture is only about O'Ol inch ; 

 for a first magnitude something much smaller than could pro- 

 bably be bored by man, or accurately measured if it could be 

 bored. With small stars of course the large telescope has, 

 with this plan, its natural advantages. For a star of the 

 fifteenth magnitude the aperture is 77 inches of an achromatic 

 object-glass ; for the fourteenth, or the next size larger, it is 

 38 inches. There is therefore a wide range of measurable 

 scale in inches against a small increase of brightness of the 

 star, and the faint light is much augmented and intensified by 

 being collected from so large an area. But this is rapidly cut 

 down as we turn to larger stars ; at the tenth magnitude the 

 aperture to be used is only 2*4 inches, so that the largest 

 instrument ever used for astronomical purposes would then 

 be not a bit better than an ordinary deer-stalking telescope 

 or a naval spyglass, and higher up it would not be so good. 



But though the defective principle of this method for na- 

 tural objects has thus been pointed out, chiefly to show the 

 direction in which future success may be gained, it is proper 

 to say that Mr Dawes' plan appears to have been mainly 

 contrived for the of&ce work, as it were, of arranging telescopic 

 stars into their classes of so called magnitude ; and for such 

 purpose it appears well adapted, and capable of introducing 

 much improvement and regularity where now there is con- 

 fusion and uncertainty. 



Expected return of Brorson's Comet. — This small body was 

 discovered by M. Brorson in 1846, and from the orbit, com- 

 puted on the observations made then, showing the very short 

 period of 1725 days, its return to perihelion is expected next 

 month. An ephemeris to guide observers in their searches 

 has been printed and distributed by the Superintendent of 

 the Nautical Almanac ; but from the low south declination 

 which he assigns the comet, it will not probably be seen in 

 the northern hemisphere. 



