[Philadelphia], “Monday, July 4 [1791], No. 96, South Street.” Apologizes for trouble given him about Irenæus and is mortified to discover his mistake. Mr. Crawford, who purchased the book, has positively assured him he mentioned Justin Martyr, not Irenæus, though, as TJ had already bought one of the two copies of Justin Martyr, he “cannot possibly account for the error.”

Having yesterday taken up Notes on Virginia and had his “imagination so hurried away by the united streams of Shenandoah and Patowmac, bursting forth at your command, as at the touch of Moses’ rod, and forcing their way through opposing mountains,” he lost sight of every consideration pointing out impropriety of asking TJ’s attention to a trifling plan which some would think useless and others impracticable. But he hopes “the philosophic writer of the Notes on Virginia will excuse me for hazarding an idea, even though it should, upon investigation, prove erroneous—and for venturing to address it to Him, in preference to men less capable of deciding on its merit.”

To keep the legislative body comfortably warm in winter presents no great difficulty. But in summer it would perhaps be desirable to keep them comfortably cool, especially if not expensive or troublesome. “Now Saltpetre is universally known to be a very powerful refrigerant: and Saltpetre will, no doubt, be among the military stores, of which government must constantly have an adequate provision. Suppose, then, that under the Rooms, which are to be erected, for … Congress, on the banks of Patowmac, space sufficient were allowed (without descending to the damp) for Magazines of Saltpetre. Communications, between these and the Rooms of Congress, might be easily contrived in a variety of modes, so as not to hurt the eye, by disfiguring the appearance of the latter. Tubes or Trunks might be fastened to the apertures underneath, and the lower end of each either lodged in a heap of the Saltpetre, or as near to it, as would be consistent with the free circulation of the air. In this case, if the windows of the rooms above were kept close shut, to exclude the warm air of the surrounding atmosphere, any accession of air, to that already contained in the rooms, must come directly through the Saltpetre, cool and fresh, and purified (I would suppose) from many of those noxious particles, of which the frost happily rids us every winter.

“In the ceiling, an opening will, no doubt, be left, for the purpose of ventilating the Rooms of Congress. Suppose, however, it were thought advisable to aid the ordinary ascensive motion of the warm air, and consequently the influx of cool air from the Saltpetre—rooms, Quære, whether—(ridiculous as the idea may, at first sight, appear to some people)—the force of fire might not be made subservient to this end? The effects of fire upon air, and (if I may be allowed to coin a new expression) the ignipetal force of the latter, are too well known, to need a demonstration. Suppose, then, that, over the aperture for ventilating the Room, there were contrived, in the roof or dome of the house, a funnel of proper dimensions, in which a stove should be placed, at such distance from the ventilator, as to attract the air through it, rather than from any other part: this stove might be kept constantly heated during the sitting of Congress in warm weather; and would thus accelerate the circulation of the whole volume of air, between the Saltpetre-rooms and the roof.”

He does not know how far it would be necessary to establish the height at which outside air should be introduced to the saltpeter area, but this could be determined by experiment, with “trunks run up (in a Northern aspect) along the walls, or funnels left open in the masonry).” Not being versed in natural philosophy, he cannot vouch for the practicability of the plan or say how far it will admit useful improvements. “With doubt and hesitation, therefore, I beg leave to present it to a philosopher, as I would present a rough stone to a skillful statuary, who can at once decide whether it is susceptible of a polish—and, if it be, can call forth, from the rude mass, a twin sister to the Medicean Venus, or a younger brother to the Apollo of Belvedere.”