MY DEAR MISS MITCHELL: ... We are much pleased to hear of your acquisition of an equatorial instrument under a revolving roof, for it is a true scientific luxury as well as an efficient implement. The aperture of your object-glass is sufficient for doing much useful work, but, if I may hazard an opinion to you, do not attempt too much, for it is quality rather than quantity which is now desirable. I would therefore leave the multiplication of objects to the larger order of telescopes, and to those who are given to sweep and ransack the heavens, of whom there is a goodly corps. Now, for your purpose, I would recommend a batch of neat, but not over-close, binary systems, selected so as to have always one or the other on hand. I, however, have been bestirring myself to put amateurs upon a more convenient and, I think, a better mode of examining double stars than by the wire micrometer, with its faults of illumination, fiddling, jumps, and dirty lamps. This is by the beautiful method of rock-crystal prisms, not the Rochon method of double-image, but by thin wedges cut to given angles. I have told Mr. Alvan Clark my "experiences." and I hope he will apply his excellent mind to the scheme. I am insisting upon this point in some astronomical twaddle which I am now printing, and of which I shall soon have to request your acceptance of a copy. There is a very important department which calls for a zealous amateur or two, namely, the colors of double stars, for these have usually been noted after the eye has been fatigued with observing in illuminated fields. The volume I hope to forward--_en hommage_--will contain all the pros and cons of this branch. There is, for ultimate utility, nothing like forming a plan and then steadily following it. Those who profess they will attend to everything often fall short of the mark. The division of labor leads to beneficial conclusions as well in astronomy as in mechanics and arts. Mrs. Smyth and my daughter unite with me in wishing you all happiness and success; and believe me My dear Miss Mitchell, Yours very faithfully, W. H. SMYTH. In regard to the colors of stars, Miss Mitchell had already begun their study, as these extracts from her diary show: "Feb. 19, 1853. I am just learning to notice the different colors of the stars, and already begin to have a new enjoyment. Betelgeuse is strikingly red, while Rigel is yellow. There is something of the same pleasure in noticing the hues that there is in looking at a collection of precious stones, or at a flower-garden in autumn. Blue stars I do not yet see, and but little lilac except through the telescope.