Capuchin monk, whose name was Cherubino, placed two telescopes together, little thinking that the moderns
Fig. 41.—The Galilean Telescope.
would imitate him in that very worldly instrument, the opera-glass.
Everybody has noticed that when objects are close to us they appear larger than when they are at a distance; it accordingly amounts to the same thing whether, in speaking of the power of telescopes, we say they magnify twice, four times, or a hundred times, or that they are brought within half, a quarter, or a hundredth of their distance. Thus there is a telescope at Lord Rosse's Observatory, at Parsonstown in Ireland, which is the finest yet constructed. Its highest magnifying power is 6,000, therefore every object we look at with it is brought within the 6,000th of its distance from us. Looking at the moon, for instance, we know that our satellite is distant some 240,000 miles from us; we have, therefore, only to divide that number by 6,000 to find that by means of this wonderful instrument the moon is brought within 40 miles of the earth. This statement, however, is not strictly true, for it supposes the whole of the apparatus used to be theoretically perfect.
Kepler, whose great name is now-a-days always associated with that of Galileo, but who during their life-time was somewhat his rival, substituted for the single lens forming the eye-piece a combination consisting of two convex lenses, in order to obtain a larger field for
