CHAPTER I.
A HALF-HOUR ON THE STRUCTURE OF THE TELESCOPE.
There are few instruments which yield more pleasure and instruction than the Telescope.

Even a small telescope--only an inch and a half or two inches, perhaps, in aperture--will serve to supply profitable amusement to those who know how to apply its powers.

I have often seen with pleasure the surprise with which the performance even of an opera-glass, well steadied, and directed towards certain parts of the heavens, has been witnessed by those who have supposed that nothing but an expensive and colossal telescope could afford any views of interest.

But a well-constructed achromatic of two or three inches in aperture will not merely supply amusement and instruction,--it may be made to do useful work.
The student of astronomy is often deterred from telescopic observation by the thought that in a field wherein so many have laboured, with abilities and means perhaps far surpassing those he may possess, he is little likely to reap results of any utility.

He argues that, since the planets, stars, and nebulae have been scanned by Herschel and Rosse, with their gigantic mirrors, and at Pulkova and Greenwich with refractors whose construction has taxed to the utmost the ingenuity of the optician and mechanic, it must be utterly useless for an unpractised observer to direct a telescope of moderate power to the examination of these objects.
Now, passing over the consideration that a small telescope may afford its possessor much pleasure of an intellectual and elevated character, even if he is never able by its means to effect original discoveries, two arguments may be urged in favour of independent telescopic observation.