Observatory of Cambridge with the necessary sums for the
construction of a gigantic optical instrument. This instrument
was designed for the purpose of rendering visible on the surface
of the moon any object exceeding nine feet in diameter.

At the period when the Gun Club essayed their great experiment,
such instruments had reached a high degree of perfection,
and produced some magnificent results. Two telescopes in
particular, at this time, were possessed of remarkable power
and of gigantic dimensions. The first, constructed by Herschel,
was thirty-six feet in length, and had an object-glass of four
feet six inches; it possessed a magnifying power of 6,000.
The second was raised in Ireland, in Parsonstown Park, and belongs
to Lord Rosse. The length of this tube is forty-eight feet, and
the diameter of its object-glass six feet; it magnifies 6,400
times, and required an immense erection of brick work and
masonry for the purpose of working it, its weight being twelve
and a half tons.

Still, despite these colossal dimensions, the actual
enlargements scarcely exceeded 6,000 times in round numbers;
consequently, the moon was brought within no nearer an apparent
distance than thirty-nine miles; and objects of less than sixty
feet in diameter, unless they were of very considerable length,
were still imperceptible.

In the present case, dealing with a projectile nine feet in
diameter and fifteen feet long, it became necessary to bring the
moon within an apparent distance of five miles at most; and for
that purpose to establish a magnifying power of 48,000 times.