FIG. 6.—LORD ROSSE'S TELESCOPE.
At first the mirrors of reflecting telescopes were made of an alloy known as speculum metal, which consisted of practically 4 parts of copper to 1 of tin; but during the last half-century this metal has been entirely superseded by mirrors made of glass ground to the proper figure, and then polished and silvered on the face by a chemical process. To the reflecting form of construction belong some of the largest telescopes in the world, such as the Rosse 6-foot (metal mirrors), Fig. 6, the Common 5-foot (silver on glass), the Melbourne 4-foot (metal mirrors, Cassegrain form), and the 5-foot constructed by Mr. Ritchey for the Yerkes Observatory. Probably the most celebrated, as it was also the first of these monsters, was the 4-foot telescope of Sir William Herschel, made by himself on the principle which goes by his name. It was used by him to some extent in the discoveries which have made his name famous, and nearly everyone who has ever opened an astronomical book is familiar with the engraving of the huge 40-foot tube, with its cumbrous staging, which Oliver Wendell Holmes has so quaintly celebrated in 'The Poet at the Breakfast Table' (Fig. 7).
FIG. 7.—HERSCHEL'S 4-FOOT REFLECTOR.
CHAPTER II
THE TELESCOPE—PRACTICAL
Having thus briefly sketched the history of the telescope, we turn now to consider the optical means which are most likely to be in the hands or within the reach of the beginner in astronomical observation. Let us, first of all, make the statement that any telescope, good, bad, or indifferent, is better than no telescope. There are some purists who would demur to such a statement, who make the beginner's heart heavy with the verdict that it is better to have no telescope at all than one that is not of the utmost perfection, and, of course, of corresponding costliness, and who seem to believe that the performance of an inferior glass may breed disgust at astronomy altogether. This is surely mere nonsense. For most amateurs at the beginning of their astronomical work the question is not between a good telescope and an inferior one, it is between a telescope and no telescope. Of course, no one would be so foolish as willingly to observe with an inferior instrument if a better could be had; but even a comparatively poor glass will reveal much that is of great interest and beauty, and its defects must even be put up with sometimes for the sake of its advantages until something more satisfactory can be obtained. An instrument which will show fifty stars where the naked eye sees five is not to be despised, even though it may show wings to Sirius that have no business there, or a brilliant fringe of colours round Venus to which even that beautiful planet can lay no real claim. Galileo's telescope would be considered a shockingly bad instrument nowadays; still, it had its own little influence upon the history of astronomy, and the wonders which it first revealed are easily within the reach of anyone who has the command of a shilling or two, and, what is perhaps still more important, of a little patience. The writer has still in his possession an object-glass made out of a simple single eyeglass, such as is worn by Mr. Joseph Chamberlain. This, mounted in a cardboard tube with another single lens in a sliding tube as an eye-piece, proved competent to reveal the more prominent lunar craters, a number of sunspots, the phases of Venus, and the existence, though not the true form, of Saturn's ring. Its total cost, if memory serve, was one shilling and a penny. Of course it showed, in addition, a number of things which should not have been seen, such as a lovely border of colour round every bright object; but, at the same time, it gave a great deal more than thirteen pence worth of pleasure and instruction.
Furthermore, there is this to be said in favour of beginning with a cheap and inferior instrument, that experience may thus be gained in the least costly fashion. The budding astronomer is by nature insatiably curious. He wants to know the why and how of all the things that his telescope does or does not do. Now this curiosity, while eminently laudable in itself, is apt in the end to be rather hard upon his instrument. A fine telescope, whatever its size may be, is an instrument that requires and should receive careful handling; it is easily damaged, and costly to replace. And therefore it may be better that the beginner should make his earlier experiments, and find out the more conspicuous and immediately fatal of the many ways of damaging a telescope, upon an instrument whose injury, or even whose total destruction, need not cause him many pangs or much financial loss.
It is not suggested that a beginning should necessarily be made on such a humble footing as that just indicated. Telescopes of the sizes mainly referred to in these pages—i.e., refractors of 2 or 3 inches aperture, and reflectors of 4½ to 6 inches—may frequently be picked up second-hand at a very moderate figure indeed. Of course, in these circumstances the purchaser has to take his chance of defects in the instrument, unless he can arrange for a trial of it, either by himself, or, preferably, by a friend who has some experience; yet even should the glass turn out far from perfect, the chances are that it will at least be worth the small sum paid for it. Nor is it in the least probable, as some writers seem to believe, that the use of an inferior instrument will disgust the student and hinder him from prosecuting his studies. The chances are that it will merely create a desire for more satisfactory optical means. Even a skilled observer like the late Rev. T. W. Webb had to confess of one of his telescopes that 'much of its light went the wrong way'; and yet he was able to get both use and pleasure out of it. The words of a well-known English amateur observer may be quoted. After detailing his essays with glasses of various degrees of imperfection Mr. Mee remarks: 'For the intending amateur I could wish no other experience than my own. To commence with a large and perfect instrument is a mistake; its owner cannot properly appreciate it, and in gaining experience is pretty sure to do the glass irreparable injury.'