A: Number. B: Focal length in inches. C: Diameter of aperture in inches. D: Prices in guineas. -----+---------+------+-----------------------------------+---- | | | | A. | B. | C. | Magnifying powers. | D. -----+---------+------+-----------------------------------+---- 1 | 3 | 1.1 | 1 Power of 18 times | 3 2 | 4-1/2 | 1.3 | 1 " 25 " | 4 3 | 7 | 1.9 | 1 " 40 " | 6 4 | 9-1/2 | 2.5 | 2 Powers 40 and 60 " | 8 5} | 12 | 3.0 | 2 " 55 and 85 " | 10 6} | 12 | 3.0 | 4 " 35, 55, 85, and 110 " | 14 7 | 18 | 3.8 | 4 " 55, 95, 130, and 200 " | 20 8 | 24 | 4.5 | 4 " 90, 150, 230, and 300 " | 35 9 | 36 | 6.3 | 4 " 100, 200, 300, and 400 " | 75 10 | 48 | 7.6 | 4 " 120, 260, 380, and 500 " | 100 11 | 72 | 12.2 | 4 " 200, 400, 600, and 800 " | 300 12 | 144 | 18.0 | 4 " 300, 600, 900, and 1200 " | 800 From this table, it appears that Mr. Short charged 75 guineas for a 3 feet reflector, whereas such an instrument is now marked in the London opticians’ catalogues at £23, when mounted on a common brass stand, and £39. 18s., when accompanied with rack-work motions and other apparatus. It is now generally understood that in the above table, Short always greatly _overrated_ the higher powers of his telescopes. By experiment they were generally found to magnify _much less_ than here expressed.