LV. An account of a memoir read at the Royal Academy of Sciences at Paris, by M. de Barros, a Portuguese gentleman, concerning certain phœnomena observed by him at Paris, in the last transit of Mercury over the Sun: by J. Short, A. M. F. R. S

The author says, he made use of an excellent Gregorian reflector of four feet in length, taking in the eye-piece, toge­ther with as much of the great tube, as exceeds the focal lengths of the two eye-glasses (I suppose it should be the two speculums ): that the focus of the great speculum is 33 (Paris ) inches; that of the small one four inches; the focus of the eye-glass next the eye 18 lines; the focus of the glass furthest from the eye 5 inches; and, lastly, that the combined power of these two glasses is nearly equal to that of a single eye-glass of 3 inches.