Page:ASC 1868 07 11 13-11.pdf/1

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19, Bloomsbury Street,
London. 11 July 1868
W. C.

Revd Sir
I have to acknowledge the receipt of your last letter, and I have since looked over my computations for the optical part of the Solar Eyepiece.

The result is as follows. I find that the entry made when I had the pleasure of seeing you, refers to a Telescope 7 feet ie 84 inches, and upon this my calculations were based - Thus, the sun's image at the focal point for a Telescope of 84 inches is .7812 and in order to be quite clear, I allowed an aperture of .9 - Now, unfortunately from your measure of the sun's image, as contained in your last letter, it is clear that your Telescope must be of longer focal