570 THE SUN A SMALL STAR. 
hole, in which a lens might be fitted, of the finest material and finish, having a focal 
distance of the one hundred-thousandth part of the whole distance between your 
eye and the lens; then by viewing through it the vertical sun, in a clear sky, you 
would see it reduced exactly as though removed 100,000 times its present distance; 
and it would barely exceed the brightness of a Lyre. 
From the great number of experiments I have made, I am led to believe this the 
most reliable method of reducing the Sun's light, for comparing it with any given 
celestial object. You can free your observation entirely from the distracting effect 
of daylight, and even an object so bright as the Sun can be reduced by one single 
plano-convex lens, at one step, to equal a star of the sixth magnitude, if desirable; 
and when the focal distance of your lens is known, and the distance between your 
lens and your eye is known, the amount of reduction can be known as readily as 
you can find how many times the smaller is contained in the larger distance. I have 
no such well or mine, but a horizontal under-ground chamber 230 feet in length, one 
end terminating in the cellar of my workshop, and the other communicating with 
the surface of the ground by a vertical opening one foot square and five feet deep, is 
a complete equivalent, except that its use involves the necessity of twice reflecting the 
Sun's light, once by a mirror, and once by a prism of total reflection. 
Between the end of the chamber and the vertical opening is a partition with a 
perforation two inches square, which I can close with plates, containing such lenses 
as I may wish to use. Within the vertical opening, contiguous to and facing the 
lens, the prism is placed to receive the Sun's light from the mirror above, and reflect 
it horizontally through the lens into the chamber. 
When a lens one thirty-fourth of an inch in focal distance was employed, on the 
24th of November, 1862, the Sun near the meridian and sky remarkably clear, by 
an observer in the cellar, 230 feet distant, the light received was estimated scarcely 
equal to that of a Lyre. 
Here the reduction of diameter was only 93,840 times, with the lens and prism 
very perfect, and cleaned for the occasion. 
Three perforations were selected through a strip of thin brass, the largest of which, 
when held to the eye, should admit light enough for steady visibility; the next, visi- 
bility by fits; and the smaller, but little less, producing invisibility. 
Three, myself and two sons, took a part in the observation, and with results show- 
ing the most perfect equality in our eyes; and when one had been in darkness for 
fifteen minutes, another fresh from the glare of day, taking his place, would see within 
two minutes as well, and as well we became satisfied, as we could with any allow- 
