Since then, it is certain some improvement has been made in the composition for lenses. In an English paper we find the following:--"One of the most remarkable optical lenses of modern manufacture is that produced by Messrs. Chance, English manufacturers, being an attempt by them to improve the manufacture of glass for optical purposes. The diameter is twenty-nine inches, and it is two inches and a quarter thick. It is really not a lens, but a plain disk intended for a lens, should its quality be sufficiently fine. The weight is about two hundred pounds. This piece of glass was inspected, on its first public exhibition, by eminent scientific judges. It was by them examined edgewise, transversely, and obliquely; it was viewed by daylight and by candle-light; it was tested by the polariscope and by other means; and after having been thus subjected to a severe ordeal, it was pronounced to be the largest and finest known specimen of the kind." The promise held out by the foregoing we fear has failed, as in very many previous cases, or the world ere this time would have heard of its success. An achromatic object-glass for telescopes consists of at least two lenses, the one made of flint-glass, and the other of crown-glass. The former, possessing least power of dispersing the colored rays relative to its mean refractive power, must be of greater value than the latter. It is upon this principle that the achromatism of the image is produced, the different colored rays being united into one focus. Flint-glass, to be fit for this delicate purpose, must be perfectly homogeneous, of uniform density throughout its substance, and free from wavy veins or cords. From the foregoing, the reader will see that, as has been said, the chief difficulty which exists in making telescopic lenses arises from want of pure glass. Every attempt to correct this evil has failed; it is well known our best telescopes and like optical instruments have always achromatic lenses, and for photographic purposes achromatic lenses are indispensable. If philosophers and astronomers have with so imperfect lenses attained so much, what may not the astronomer look for when science gives him lenses made from pure glass? If the heavens, by imperfect instruments, have so far been unveiled, to what extent may he not then be able to penetrate the pure ether, and reveal planets and heavenly bodies as yet unknown?