Page:ASC 1853 09 08 13-51.pdf/1

Dear Sir
I have much pleasure in acknowledging the receipt of your very interesting letter, and return to you my sincere thanks for it. I began a reply to it more than a month ago, but was suddenly obliged to leave home, and I regret that, in consequence of illness since my return, I have been till now unable to resume my pen.
I am very glad to learn that you were able to pay continued attention to Saturn throughout his last apparition. Your observations are extremely valuable, and will be thankfully received by our Astronomical Society. There can be no reasonable doubt of the great excellence of your large Munich Equatorial; and the observations you have made with it are evidently of great weight.
I was not aware that you were paying so particular attention to the projection of the southern edge of the ball on to the rings, with a view to mark its exact place. - The only occasion when I judged it to be quite clear of the division between A and B was on 26 Sept. 1854; and on that night I entered in my journal as follows: - "The division between A and B is seen to extend all 'round at both the north and south points of the ball, which does not seem to me to encroach on it at all, though it certainly touches it on the southern side. The diameter of the ball therefore from north to south appears to the exactly equal to the minor axis of the exterior edge of B." - This was evidently a careful observation: - but I have also recorded respecting the state of the air; "The air is not in a fine state; yet occasionally the views are sharp for several seconds together, though considerable tremor is always present." - The highest power I was able to use with sufficient

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