Dr. Herschei/s Observations of the Transit of Mercury, &c. 215 
attention to the contour of the mercurial disk, and found its 
termination perfectly sharp. 
With a 10-feet reflector, and magnifying power of 130, I 
saw the corrugations of the luminous solar surface, up to the 
very edge of the whole periphery of the disk of Mercury. 
io h 27'. When the planet was sufficiently advanced towards 
the largest opening of the northern zone, I compared the in- 
tensity of the blackness of the two objects ; and found the disk 
of Mercury considerably darker, and of a more uniform black 
tint, than the area of the large opening. 
io h 32'. The preceding limb of Mercury cuts the luminous 
solar clouds with the most perfect sharpness ; whereas, in the 
great opening, the descending parapet, down the preceding side, 
was plainly visible. 
It should be remarked, that the instrument here applied to 
the sun, with the moderate power of 130, is the same 10-feet 
reflector which, in fine nights, when directed to very minute 
double stars, will show them distinctly with a magnifier of 1000. 
Having often attempted to use high magnifiers in viewing the 
sun, I wished to make another trial ; though pretty well assured 
I should not succeed, for reasons which will appear hereafter. 
With two small double convex lenses, both made of dark- 
green glass, and one of them having the side which is nearest 
the eye thinly smoked, in order to take off some light, I viewed 
the sun. Their magnifying power was about 300 ; and I saw 
Mercury very well defined; but that complete distinctness, which 
enables us to judge with confidence of the condition of the 
object in view, was wanting. 
With a single eye-glass, smoked on the side towards the eye, 
and magnifying 460 times, I also saw Mercury pretty well 
