Ditto, with rack-work motions, improved mounting, and metals 39 18 Two feet long without rack-work, and with 4 magnifying powers, improved 15 15 Ditto with rack-work motion 22 1 Eighteen inch on a plain stand 9 9 Twelve inch Ditto 6 6 The above are the prices stated in Messrs. W. and S. Joneses catalogue. The following list of prices of the various kinds of reflecting telescopes is from Messrs. Tulley’s (of Islington) catalogue. £ _s._ 1 foot _Gregorian_ reflector, on pillar and claw stand, metal 2-1/2 inches diameter, packed in a mahogany box 6 6 1-1/2 foot ditto, on pillar and claw stand, metal 3 inches diameter, packed in mahogany box 11 11 2 feet ditto, metal 4 inches diameter 16 16 Ditto, ditto, with rack-work motions 25 4 3 feet ditto, metal 5 inches diameter, with rack-work motions 42 0 Ditto, metal 6 inches diameter, on a tripod stand, with centre of gravity motion 68 5 4 feet ditto, metal 7 inches diameter, as above 105 0 6 feet ditto, metal 9 inches diameter, on an improved iron stand 210 0 7 feet _Newtonian_ reflectors, 6 inches aperture, mounted on a new and improved stand 105 0 Ditto, ditto, metal 7 inches diameter 126 0 9 feet ditto, metal 9 inches diameter 210 0 10 feet ditto, metal 10 inches diameter 315 0 12 feet ditto, metal 12 inches diameter 525 0 _Comparative brightness of achromatic and reflecting telescopes._ The late astronomer royal, Dr. Maskelyne, from a comparison of a variety of telescopes, was led to the following conclusion,--‘that the aperture of a common reflecting telescope, in order to show objects as bright as the achromatic must be to that of an achromatic telescope as 8 to 5,’--in other words, an achromatic whose object glass is 5 inches diameter, will show objects with as great a degree of brightness as a reflector whose large speculum is 8 inches in diameter. This result, if correct, must be owing to the small number of rays reflected from a speculum compared with the number transmitted through an achromatic object glass. SECT. 2.--THE HERSCHELIAN TELESCOPE.