Pg ee Rogen aio ier 
Sree he es, 
A. Clark on the Sun and Stars photometrically pee 81 
when the slightest ray is again allowed to enter past the pet. 
it is reflected from the lens, and combining with the light trans- 
mitted from the sun becomes conspicuous as before. 
This I have found to be the case when neither the transmitted 
nor the reflected light — could stimulate the visual organs 
to a recognition of its prese 
ince noticing this fact, I pret e close every avenue to the 
admission of light about the he ad, preparatory to the final effort, 
and if the sun is not seen within five min utes, I give it up, 
reduce the distance between the lenses about one- twentieth, and 
tained estimated equal to a faint sixth magnitude, the distance 
between the lenses is measured, and the reducing power com- 
puted. Ido not, it will be seen, trust to any comparisons with 
artificial lights as standards, but make a minimum visibile the 
standard in all cases; which leaves the eyes and attention free 
to pursue one object. at atime. A movable brass plate, peas a 
perforation one-tent th of an inch in diameter, is 
inches beyond the lens next the sun, for adantting his direct 
ee with only a very narrow annulus of surrounding sky- 
The following results were obtained April 28. 
6h 30™ a. M. 1,055,360 — sky admitted. 
6 40 783, sky screened off. 
12 noon, 1,308,000 sky screened off. 
12 10 PM. 1,574,400 — sky admitted. 
These morning observations were made for the benefit of a 
: ae who wished them for a special pu 
Tpose. 
numbers in the noon observation are very near the max- 
_ imum exhibited in = extreme efforts, made when the skies 
_ Were remarkably cle 
Am. Jour. Sor.—SEconD iii Vou. XXXVI, No. 106.—Juxy, 1863, 
il 
