For the information of amateur constructors of telescopes, I shall here state the dimensions of two or three four glassed eye-pieces in my possession, which perform with great distinctness, and present a pretty large field of view. In one of these, adapted to a 44-1/2 inch achromatic, the lens A, next the object, is 1-7/8 inch, focal length, and about 1 inch diameter, with the plane side, next the object. The focal length of the lens B 2-1/10 inches, diameter 7/10 inch, with its plane side next A; distance of these lenses from each other 2-4/10 inches. Distance of the field lens C from the lens B 5-1/2 inches. The small hole or diaphragm between A and B is at the focus of A, and is about 1/6 inch diameter, and about 3/8 of an inch from the lens B. The field lens C is 2 inches focal length, and 1-1/4 inch diameter, with its plane side next the eye. The lens next the eye D is 1 inch focal distance, 1/2 inch diameter, and is distant from the field glass 1-3/4 inch, with its plane side next the eye. The magnifying power of this eye-piece is equivalent to that of a single lens whose focal length is half an inch, and with the 44-1/2 inch object glass produces a power of about 90 times. The lens next the eye can be changed for another 1-3/8 inch focal length, which produces a power of 65; and the two glasses CD can be changed for another set, of a longer focal distance which produces a power of 45 times. The whole length of this eye-piece is 11-1/2 inches. In another eye-piece, adapted to a pocket achromatic, whose object glass is 9 inches focal length, the lens A is 1 inch focal length, and 1/2 inch diameter; the lens B 1-1/4 inch, and 1/2 inch diameter, their distance 1-1/2 inch, the lens C 1-1/10 inch focal length, and 5/8 inch diameter; the eye-lens D 5/8 inch focal length, and 3/8 inch diameter; distance between C and D 1-1/8 inch. The distance between B and C 1-3/4 inch. The whole length of this eye-piece is 4-1/2 inches, and its power is nearly equal to that of a single lens of 1/2 or 6/10 of an inch focal length, the magnifying power of the telescope being about 16 times. Another eye-piece of much larger dimensions, has the lens A of 2-1/2 inches focal length, and 3/4 inch diameter: the lens B 2-3/4 inches focus and 5/8 inch diameter; and their distance 2-3/4 inches; the lens C 2-5/8 inches focus and 1-1/8 inch diameter; the lens D 1-3/4 inch focus and 3/4 inch diameter; distance from each other 2-3/4 inches. The distance between the lenses B and C is 4 inches. The magnifying power is equal to that of a single lens 1-1/8 inch focal distance. When applied to an achromatic object glass 6 feet 7 inches focal length, it produces a power of about 70 times. This eye-piece has a moveable tube 9 inches in length in which the two lenses next the eye are contained, by pulling out which, and consequently increasing the distance between the lenses B and C, the magnifying power may be increased to 100, 120 or 140, according to the distance to which this