II. A letter from Mr. Dawes to Mr. Herschel, giving observations of the double stars, 70 Ophiuchi, ; Ursae Majoris, 44 Bootis, Virginis, and Coronae, Castor, Leonis, and Bootis, made during the last and present year. Mr. Dawes is of opinion that the apparent discs are more affected by the aperture of the telescope than by any other circumstance ; and that this is the principal reason why a reflector presents a smaller image of a fixed star than an achromatic of equal illuminating power