I have been honored with your letter of the 29th: of Decr., though it arrived four weeks after its date. The very day after I received it, I began a long answer, which only waits for Messrs. Nairne & Blunt’s execution of what is mentioned in it, to be forwarded to you through Col. Smith; for it is too bulky for the post. I hope it will leave my hands tomorrow, and convince you of the anxiety I have to attend to any communication or directions you may think proper to favor me with.

It is very true that Dr. Herschell has discovered two satellites to the Georgium Sidus; one revolving in about a week, the other in about a fortnight; but by his account to us their orbit does not seem favorable for affording us eclipses. He discovered them last month by means of some new advantages he had given to one of his instruments, for he had never been able to discover them before. His great instrument will still take some little time to perfect; and it is hard to say what is not to be expected from it, if it succeeds. He will have all the world before him, and a certainty that nobody can for some time have the same advantages. This is a more honest monopoly than some others that could be named. I am happy that these satellites are not to be discovered without the best instruments, for it will be a criterion to the instruments of every country and a disgrace to those that are deficient, which will tend to the improvement of astronomy generally, and little be lost with respect to the present object, which seems most interesting at present as a spectacle of curiosity.

Dr. Herschell has promised me an account of these satellites for the Philadelphian Philosophical Society, of which he has lately been elected member.

I know of nothing very mate[rial] here at this moment, (which you are [not] likely to learn from other quarters,) on other subjects. I have the honor to be, with great respect & esteem, Your Excellency’s Most obedient & most humble servt.,