that of refractors of equal size, and for anything like 3 feet very much greater.” He nearly obtained the order for a monster reflector for the Lick Observatory, the Americans admitting that the reflector must be the instrument of the future for power and light because there were practically no limits to its size. But the reflector has not been much used in America, and therefore is little known. For this reason the authorities decided to erect a large refractor, and they appear to have been justified in their selection, for the 36-inch objective has proved excellent. FOOTNOTES: [5] Such objects show considerable glare in a very large instrument. The advent of Jupiter into the field of the 6-foot has been compared to the brightness of a coach-lamp. The outer satellite of Mars was seen twice with this instrument in 1877, “but the glare of the planet was found too strong to allow of good measures being taken.” CHAPTER III. _NOTES ON TELESCOPES AND THEIR ACCESSORIES._ Choice of Telescopes.—Refractors and Reflectors.—Observer’s Aims.—Testing Telescopes.—Mounting.—Eyepieces.—Requisite Powers.—Overstating Powers.—Method of finding the Power.—Field of Eyepiece.—Limited Means no obstacle.—Observing-Seats.-Advantage of Equatoreals.—Test-Objects.—Cheapness and increasing number of Telescopes.—Utility of Stops.—Cleaning Lenses.—Opera-Glasses.—Dewing of Mirrors.—Celestial Globe.—Observatories. _Choice of Telescopes._—The subject of the choice of telescopes has exercised every astronomer more or less, and the question as to the best form of instrument is one which has occasioned endless controversy. The decision is an important one to amateurs, who at the outset of their observing careers require the most efficient instruments obtainable at reasonable cost. It is useless applying to scientific friends who, influenced by different tastes, will give an amount of contradictory advice that will be very perplexing. Some invariably recommend a small refractor and unjustly disparage reflectors, as not only unfitted for very delicate work, but as constantly needing re-adjustment and resilvering[6]. Others will advise a moderate-sized reflector as affording wonderfully fine views of the Moon and planets. The question of cost is greatly in favour of the latter construction, and, all things considered, it may claim an unquestionable advantage. A man who has decided to spend a small sum for the purpose not merely of gratifying his curiosity but of doing really serviceable work, must adopt the reflector, because refractors of, say, 5 inches and upwards are far too costly, and become enormously expensive as the diameter increases. This is not the case with reflectors; they come within the reach of all, and may indeed be constructed by the observer himself with a little patience and ingenuity.