164 Divisibility of Matter. 
eye at the distance of nine inches. Here I would just observe, that 
the candle was supposed to be so philosophically made, that, whilst 
it maintained a constant bright flame, it did not intercept its light 
from a single letter in the concave sphere. 
Again, the light, reflected from a single letter, would render that 
letter visible to an eye at the distance of nine inches not in one di- 
rection only, but to an eye placed any where in the concave sur- 
face of a hemisphere of nine inches radius. ‘To how many eyes 
then, is the light reflected from one letter, sufficient to render it 
visible ? 
I supposed the pupil of the eye to be one eighth of an inch in di- 
ameter, which is probably near the truth. On this supposition, the 
surface of a hemisphere of nine inches radius is equal to the pupils 
of forty one thousand four hundred and sixty five eyes. To this 
number of eyes, or to half this number of pairs of eyes, the light re- 
flected from a single letter is sufficient to render that letter distinct- 
ly visible. But here it may be objected, and it is true, that to an 
eye, placed near the plane of the leaf, a sufficiency of light would 
not be reflected. But it is also unquestionably true, that not half 
the light, which falls upon the leaf, is reflected. ‘The light, there- 
fore, which is absorbed, would much more than compensate for this 
deficiency. , 
Now, the light, which falls upon a single letter, being sufficient to 
render it visible to 20,732 pairs of eyes, and the number of letters in 
the concave surface of a sphere of three feet radius being 6,514,400, 
the light which falls upon all these letters is sufficient for 1385,056,- 
540,800 pairs of eyes, or the light of one candle, should not a par- 
ticle be lost, and the whole be so distributed, that each should re- 
ceive his equal portion, is sufficient to enable 135,056,540,800 per- 
sons to read at the same time. If our earth contains 900,000,000 
of inhabitants, and that, I believe, is the highest supposition ever 
made, the light of one candle is more than sufficient to enable all 
the inhabitants of one hundred and fifty such worlds to be reading 
at the same instant. ‘This conclusion, | am aware, will appear to 
many, perhaps to most, altogether incredible. But any one, pos- 
sessing but a moderate share of mathematical knowledge, may ina 
short time easily satisfy himself, that rejecting fractions, it is rigidly 
exact. 
A candle like that, to which I have referred, would undoubtedly, 
continue burning at least four hours. What quantity of light then, 
