82 A. Clark on the Sun and Stars photometrically compared. 
It makes an enormous difference, it will be noticed, whether 
the sun is observed with the atmospheric light sereened off or 
not; but, to give the sun and the star equal conditions, the eye 
should in both cases be shielded against the light from surround: 
ing regions. If we could condense into a compass of less than 
the fourth of a second all the sky-light within 40° of a faint star, 
and add it to the star, it would give a manifold increase to its 
brightness. This is what occurs in observing the sun without 
the screen; though the atmospheric light in question is, by day, 
m the sun alone, but night, from the host of stars of all — 
in both cases as effectually as possible. The method by which — 
it is cleared from the sun is already explained; but for dealing — 
with a star, I remove all the lenses from the finder tube to my 
nine times as much as could possibly be required, so far as I cat 
understand by these experiments, to give him companionship 
with the star 32 Bootis. 
Cambridgeport, May 26, 1863. ‘ 
