largest existing achromatic telescope in the world. It was like a horse gaining a race by the fraction of a neck. Mr Clarke's lens distances all competitors, as its area is half as large again as that of the Cambridge equatorial. The glass was from Chance, Birmingham, and no defect could be traced in it. The figure and polish seemed also perfect, but the performance can never be confidently predicted before actual trial. The character of Mr Clarke as an optician, however, gives good ground for the belief that it will far surpass anything that has been yet attempted.
Telescopes, like guns, are rated according to their calibre. Everything depends on the size of the lens, all else being equal. The difficulty of obtaining good glass, and working the lens, increases enormously with the size. The rate is something like that of the speed of a steamer. Every successive knot per hour requires a rapidly increasing rate of expenditure of fuel; and every increase of the size of the object-glass implies a much higher proportion of trouble and expense. The difficulties increase so rapidly, that in the workshops even of Munich, nothing greater than fifteen inches would be attempted. All honour to the courageous attempt of Mr Clarke! The astronomical world will not grudge America this triumph. She has unexpectedly taken the lead in various departments of practical astronomy; and it will be somewhat singular if a self-
