Royal Socvety of London. 363 
of it, that shines upon us from any one, even the most brilliant, of the 
fixed stars. 
“It may be remembered, that on a former occasion, in examining 
the performance of a good. telescope, I found that the sun’s image, 
reflected from the surface of a small sphere, (such as that of a ther- 
mometer bulb, filled with mercury,) and viewed at a proper distance 
through a telescope, is, to all appearance, extremely like a fixed star, 
and forms in such experiments, an admirable substitute for one, in 
being really fixed, and therefore well adapted for deliberate obse1va- 
tion. It occurred to me, while engaged in this examination, that. by 
comparing such an image with one of the larger stars, I might be able. 
to obtain some grounds for estimating the light of the star... 
“It would be desirable, though extremely difficult, in conducting such 
an experiment, to make a direct comparison between the star and the 
sun’s image; since in that case we should be enabled. to avoid the 
uncertainties arising from an indirect comparison, the consequence of 
observing at times so distant, that the atmosphere has. in the interval 
undergone considerable changes. As, however, the only practicable 
mode of observing is the indirect one, by comparing the two objects 
with some common standard at different times, we must: endeavor. to 
remove these uncertainties from our results, by repeating each series 
of comparisons so frequently, that the average of each series may be 
affected by atmospheric vicissitudes, or may fairly be presumed.to. be 
so, in an equal degree. Sinan ali git 
_ The common standard of comparison I chose, was the image: of 
a candle, reflected from a small thermometer bulb, (in most trials, 
about one quarter of an inch in diameter) filled with mercury,..and. 
seen by one eye through a lens of about two inches. focus; at the 
same time that the sun’s image, (reflected in a similar manner,) from 
-a thermometer bulb, placed at a distance, was viewed. by the other 
eye through a telescope.” aR 
The precautions used, and the detail of the observations, would 
exceed our limits; we shall therefore pass to the resu These 
are: that the light of the brightest. of the stars, Sirius, does not ex- 
ceed a 20,000,000,000th part. of the sun’s light ; and that of Lyra 
is about the 180,000,000,000th part of the same, or one-ninth part 
of the light that reaches us from Sirius. Ee 
The fourth paper of Wollaston is stated by him, to be communt- 
cated for the purpose of doing justice to the memory of Dr. Marcet, 
by recording one of his latest efforts in the cause of science. It is 
well known that a current, at the surface, is continually setting 
