562 Philosojphical Transactions of the 



The second paper is also by the same author, and contams an ac- 

 count of a microscopic doublet. Adopting the principle employed in 

 the form of the eye piece used in telescopes, and called Huygenian, 

 he forms his magnifier of two plano-convex lenses. This plan he in- 

 ferred would obviate both the spheric and chromatic aberration, and 

 produce a much more distinct image than has yet been attained in 

 any other manner. These anticipated advantages were fully real- 

 ized in practice, and he states that he was enabled, by the aid 

 of a microscope constructed upon this principle, to view the most 

 minute objects, with " a degree of delicate perspicuity he had in vain 

 sought in any other microscope with which he was acquainted." 



The next of Wollaston's papers contains an account of a method of 

 comparing the light of the sun with that of the fixed stars. It is 

 founded upon a suggestion of the Rev. John Mitchell, published as 

 long since as towards the close of the last century, but which was rude 

 and imperfect in the hands of the inventor, and has not been since used 

 by any other person. The distance of the fixed stars is a problem the 

 solution of which has escaped the ordinary direct modes of investiga- 

 tion. The search after their annual parallax led at first to the dis- 

 covery of other and far more important irregularities by which it is 

 cloaked ; and the best instruments, that the present state of the arts 

 has supplied, have left the question, whether it is of such magnitude 

 as to be detected or not, unsettled. Pond, observing with the two 

 magnificent murals of the Greenwich observatory, conceives that this 

 parallax is imperceptible, while Brinkley, an astronomer not less ac- 

 tive and zealous, but furnished with less perfect instruments, thinks 

 that he has detected it. In the absenpe of this direct method, the 

 proportion which the light, afi:brded to us separately by each of the 

 fixed stars, bearsto the light of the sun, furnishes the best, and perhaps 

 the only method within our reach, of obtaining a probable estimate of 

 their distances. The manner in which this principle was applied by 

 WoUaston, will be best explained by quoting his own words : 



" From a comparison which 1 made in the year 1799, of the light 

 of the sun with that of the moon, I should estimate the direct light of 

 the sun, as being nearly one million times greater than that of the 

 moon ; and consequently, the direct light of the sun as very many 

 million times greater than that afforded by all the fixed stars collect- 

 ively. Such then being, to our visual organs, the vast disproportion 

 in radiance between the sun and the whole starry firmament, it is not 

 to be expected that we should assign very accurately how much 

 greater the light of the sun is than that exceedingly minute quantity 



