Breadth of Ditto. 0 55 Focal distance of the lens next the eye 0 6 Breadth 0 43 This glass is plane on the side next the eye. Distance between the third and fourth glasses. 1 1 From the figure and description, the reader will be at no loss to perceive how the magnifying power is ascertained by this eye-piece. If the lowest power for a 44 inch telescope be found to be 100, when the three sliding tubes are shut into the larger one, then by drawing out the tube next the eye 4 divisions, a power of 140 is produced; by drawing out the tube next the eye its whole length, and the second tube to the division marked 220, a power of 220 times is produced, and drawing out all the tubes to their utmost extent, as represented in the figure, a power of 400 is obtained. These powers are by far too high for such a telescope, as the powers between 300 and 400 can seldom or never be used. Were the scale to begin at 50, and terminate at 200, it would be much better adapted to a 3-1/2 feet telescope. Each alteration of the magnifying power requires a new adjustment of the eye-piece for distinct vision. As the magnifying power is increased, the distance between the eye-glass and the object-glass must be diminished. Dr. Kitchener says, that ‘the pancratic eye tube gives a better defined image of a fixed star, and shows double stars decidedly more distinct and perfectly separated than any other eye tube, and that such tubes will probably enable us to determine the distances of these objects from each other, in a more perfect manner than has been possible heretofore.’ These tubes are made by Dollond, London, and are sold for two guineas each. But I do not think they excel, in distinctness, those which are occasionally made by Mr. Tulley and other opticians. CHAPTER VI. MISCELLANEOUS REMARKS IN RELATION TO TELESCOPES. The following remarks, chiefly in regard to the manner of using telescopes, may perhaps be useful to young observers, who are not much accustomed to the mode of managing these instruments.