"C" street is three times as far from the light as "A" street; hence it will be nine times darker there, for 3 × 3 = 9. This page in order to be readable there, would then have to cover nine times the space it occupies now.
The next street, being four times as remote from the light as "A" street, our letters, according to the rule given above, would have to cover sixteen times the present space, for it is sixteen times darker there than on "A" street.
"E" street, which lies at five times the distance from the light, will be twenty-five times darker, for 5 × 5 = 25. "F" street, which is six times the distance, we shall find thirty-six times darker; and, lastly, "G" street, seven times the distance from the light, will be forty-nine times darker than "A" street, because 7 × 7 = 49. The letters of a piece of writing, in order to be legible there, must cover forty-nine times the surface that our letters cover now.
But the reader will exclaim: "This evil can be remedied. We need but place forty-nine lights on Trinity steeple; there will then be sufficient light on "G" street for any newspaper to be read." Our friend will easily perceive, however, that it is more judicious to distribute forty-nine lights in different places on Broadway, than to put them all on one spot.
This is sufficient to convince any one that we may be able to illuminate large public places with one light, but not the streets of a city, and still less whole cities.
CHAPTER II.
ILLUMINATION OF THE PLANETS BY THE SUN.
It was demonstrated above, that it is impossible to illuminate large distances by a single light. Yet we must acknowledge that nature herself does this, and that the sun is the only light which shines throughout the solar system; for the light which is seen in the planets is but light received and reflected from the sun.
This is sufficient reason for us to believe, that there are not on every planet creatures as we see them on our earth; but that, on the contrary, each celestial body may be inhabited by creatures organized according to the distance of the planet from the sun; that is, adapted to the degree of light produced there by the sun.