Under the Building lately erected by the Philosophical Society there are very large and deep Cellars. Suppose in the midst of one of them, another of 12 or 15 feet deep and 16 feet square was dug and walled and arched over would it not answer the purpose of which we were speaking. A considerable part of the Expence would be saved, and whatever reasonable compensation should be made to the Society wou’d I think be very acceptable. I am a little apprehensive of one inconvenience, whether the Cavern be made there or elsewhere, I mean Mephitic Air taking possession of it, but this may be guarded against. The prodigious extent of those under the Observatory at Paris perhaps secures them from anything of that sort.—I am Dr. Sir, with great respect Yours &c.