Comparison of Sun and Stars. 61 



the focal image produced by a convex lens corresponds in appa- 

 rent magnitude and brightness with the original object when 

 viewed from a distance equal to the focal length of the lens, and 

 diminishes in proportion as the distance of the eye increases, he 

 proceeds to apply it experimentally in the following manner : — 

 Having an underground dark chamber, 230 feet in length, 

 communicating at one extremity with the open air by a verti- 

 cal opening, he first reflects the sun's rays down this opening 

 by an ordinary mirror, and then gives them a horizontal direc- 

 tion by means of a reflecting prism, on the inner face of which 

 is cemented a little convex lens of -^V of an inch focus. When 

 the solar light is transmitted through this apparatus, an observer 

 at the other end of the long gallery sees it reduced 55,200 times, 

 in which condition its appearance differs but little from that of 

 Sirius. The intention, however, being to obtain not a compara- 

 tive but an absolute reduction to the minimum visibile, or the 

 equivalent of a faint 6 mag. star, another lens of 6 inches focus 

 is interposed between the eye and the minute lens, and made by 

 means of cords to traverse the long chamber at the observer's 

 pleasure, till the solar image, thus doubly diminished, is on the 

 point of disappearance. The reduction obtained in this way, 

 amounting to 1,203,360 times, indicates that the sun, at that 

 distance, would be only just visible to the unassisted eye ; while 

 at 100,000 times his present distance, he would merely rank as 

 a pretty bright first -magnitude star, though his parallax would 

 be double that assigned to any star in the whole heavens. And 

 hence he draws the following conclusion : — " If the distances 

 imputed to several of the stars from parallax can be true, I 

 am sure those having the taste, talent, and leisure necessary 

 for following up photometrical researches with efficiency, cannot 

 fail to find our glorious luminary a very small star ; and to the 

 human understanding, thus enlightened, more than ever must 

 the heavens declare the glory of God.-" In confirmation of this 

 result he subsequently removed the 8-inch object-glass from the 

 tube of his equatoreal, and turned the eye-end to the sun, car- 

 rying two lenses of -^th and -^ th of an inch focus, at an ad- 

 justable distance from each other, and thus found, when his face 

 was inserted in place of the object-glass, a reduction of about 

 1,308,000 times necessary to obtain the minimum visibile ; a 

 result sufficiently accordant with the former, when the very 

 delicate nature of the investigation is considered. In tho 

 interesting paper, of which this is an abstract, the ingenious 

 author has taken into account the loss of light in reflexion, and 

 its increase from the strongly illuminated neighbourhood of the 

 sun ; and seems to have used every precaution in the conduct 

 of his experiments. He adds that a similar mode of reduction 

 brings the star Castor to the same point at a distance repre- 



