In viewing the _Nebulæ_, and the very small and immensely distant fixed stars, which require much light to render them visible, a large aperture of the object-glass or speculum, which admits of a great quantity of light, is of more importance than high magnifying powers. It is light chiefly, accompanied with a moderate magnifying power, that enables us to _penetrate_ into the distant regions of space. Sir W. Herschel, when sweeping the profundities of the Milky way, and the Hand and Club of Orion, used a telescope of the Newtonian form, 20-feet focal length, and 18-7/10 inches diameter, with a power of only 157. On applying this telescope and power to a part of the _Via Lactea_, he found that it completely resolved the whole whitish appearance into stars, which his former telescopes had not light enough to effect; and which smaller instruments with much higher magnifying powers would not have effected. He tells us, that with this power, ‘the glorious multitude of stars,’ in the vicinity of Orion, ‘of all possible sizes, that presented themselves to view, was truly astonishing, and that he had fields which contained 70, 90 and 110 stars, so that a belt of 15 degrees long, and 2 degrees broad, which passed through the field of the telescope in an hour, could not contain less than fifty thousand stars that were large enough to be distinctly numbered.’ In viewing the Milky way, the Nebulæ, and small clusters of stars, such as _Præsepe_ in Cancer, I generally use a power of 55 times, on an achromatic telescope 6 feet 6 inches in focal length, and 4 inches diameter. The eye-piece, which produces this power--which I formed for the purpose--consists of two convex lenses, the one next the eye 3 inches focal length, and 1-2/10 inch diameter, and that next the object 3-1/2 inches focus, and 1-4/10 inch diameter, the deepest convex surfaces being next each other, and their distance 1/4 inch. With this eye-piece a very large and brilliant field of view is obtained; and I find it preferable to any higher powers in viewing the nebulosities, and clusters of stars. In certain spaces of the heavens, it sometimes presents in one field, nearly a hundred stars. It likewise serves to exhibit a very clear and interesting view of the full moon.