contrast to the flaring, indefinite forms often seen in big telescopes. _Cleaning Lenses._—As to wiping objectives or mirrors, this should be performed not more often than absolute necessity requires; and in any case the touches should be delicate and made with materials of very soft texture. The owner of a good objective should never take the handkerchief out of his pocket and, in order to remove a little dust or dew, rub the glass until the offensive deposit is thought to be removed. Yet this is sometimes done, though frequent repetition of such a process must ultimately ruin the best telescope notwithstanding the hardness of the crown glass forming the outer lens of the objective. It will not bear such “rough and ready” usage and in time must show some ugly scratches which will greatly affect its value though they may not seriously detract from its practical utility. Good tools deserve better treatment. When the glass really wants cleaning, remove it from the tube and sweep its whole surface gently with a dry camel’s-hair brush, or when this is not at hand get a piece of linen and “flick” off the dust particles. Then wipe the lens, as soon as these have been dislodged, with an old silk, or soft cambric handkerchief; fine chamois leather is also a good material, and soft tissue paper, aided by the breath, has been recommended. But whatever substance may be adopted it must be perfectly clean and free from dust. When not in use it should be corked up in a wide-necked bottle where it will be safe from contact with foreign particles. In the case of mirrors there is an obvious need that, when being repolished, the material used should be perfectly dry and that the mirror also should be in the same state. It is unnecessary to say here that in no case must the silver film be touched when it is clouded over with moisture. This must first be allowed to evaporate in a free current of air or before a fire; the former is to be preferred. A suitable polishing-pad may be made with a square piece of washleather or chamois in which cotton-wool is placed and then tied into a bag. This may be dipped into a little of the finest rouge, and its employment will often restore a bright surface to the mirror. But the latter should be left “severely alone” unless there is urgent occasion to repolish it, as every application of the rouged pad wears the film and may take off minute parts of it, especially when dust has not been altogether excluded. The precarious nature of the silvered surface undoubtedly constitutes the greatest disadvantage of modern reflectors. The polish on the old metallic mirrors was far more durable. Some of Short’s, figured 150 years ago, still exist and are apparently as bright as when they were turned out of the workshop! I have a 4-inch Gregorian by Watson which must be quite a century old, and both large and small specula seem to have retained their pristine condition.