[ 19 ] 



IV.—On a method of comparing the light of the sun with that of the fixed stars. 

 By William Hyde Wollaston, 3I.D. F.R.S. 



Read December 11, 1828. 



One of the most ingenious contributors to the Transactions of our Society 

 in the last century, the Rev. John Michell, in a paper intituled " An inquiry 

 into the probable parallax and magnitude of fixed stars, &c*." has proposed it 

 to astronomers, as an object worthy their attention, to determine what propor- 

 tion the light, afforded us separately by each fixed star, bears to the light 

 which we receive from the sun ; since, from our inability to measure the annual 

 parallax of those very remote bodies, such a comparison is the best, perhaps 

 the only method within our reach, of obtaining, though not certain, yet pro- 

 bable estimates of their distances ; and thus forming reasonable conjectures 

 concerning the extent of the visible universe. In order that we may judge, 

 with the least chance of error, of the mean distance of those stars which are 

 the nearest to the earth, he directs us to compare the light of the brightest 

 stars with that of the sun, and next to calculate how far the sim must be re- 

 moved, to make the light that we should then receive from him, not more than 

 equal to the mean light of the stars chosen for comparison. 



Mr. Michell made, as he says, some rude experiments for determining the 

 comparative brilliancy of certain principal stars ; but has not suggested any con- 

 trivance for comparing a star with the sun. He states, however, so distinctly the 

 great object of such a comparison, and the inferences which an industrious ob- 

 server would thence be entitled to draw, concerning the distances of those stars 

 whose light he might succeed in measui-ing, that it is surprising that no astrono- 

 mer has been incited by these remarks to devise a method of making the requisite 

 observations, and that now, so many years after Mr. Michell's suggestion was 

 made public, so much remains to be eficcted in this branch of photometry. 



* Phil. Trans. 1767: p. 234. 



d2 



