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French physician and politician (1738-1814) whose name became synonymous with the 'humane' instrument of execution whose use he proposed to the government during the French Revolution. LS in French, signed “Guillotin,” four pages on two adjoining sheets, 7 x 9, July 19, 1788. Letter headed, "Report on the heat regulator adapted for bathtubs by Mr. Bonnemain, physicist," in part (translated): "In your meeting at the start of the month, on Wednesday the 2nd of this month of July 1788, Mr. Bonnemain, physicist, requested the appointment of several commissioners to examine the effect of his heat regulator, which he has applied to bathtubs for the purpose of preparing baths at a constant temperature maintained for several hours in a bathtub of seven or eight buckets of water, which in an hour and a half of time can be heated to 22, 26, or 30 degrees on a good thermometer, well calibrated for standing in the water…
Having gone to the inventor’s house, we recognized that this regulator is based on the known effects of the dilatability of metals in accordance with their density, as the expert Diemerbroek revealed by the experiments done with his pyrometer, which convinced him that with one wick, iron expands by 80 degrees, copper by 89, and brass by 110, and with five wicks, iron expands by 230 degrees, copper by 310, and brass by 377…
Mr. Bonnemain, who has a taste for experimental physics and the sagacity to carry out his experiments, having observed how difficult it is to keep hot baths at a constant temperature, in order to better satisfy the aims of the doctors who prescribe them and to forestall the effects of the unskillfulness of some of those who care for the sick and the inattentiveness of domestic servants, has adapted his pyrometer or heat regulator for bathtubs, with the exclusive privilege that he has been awarded on the recommendation of the Academy of Sciences.
A copper pipe crosses the bottom of the bathtub. On its upper third, on the outer side, there is a moveable dial that should stop when the lever completely closes the grate and only lets pass a very weak air current, sufficient to keep the fire in the furnace from going out entirely and maintain the desired temperature. If this is not the case, the regulator cools, the lever rises, and the influx of a stronger air current revives the fire and quickly returns the bath to the same temperature.
If one wishes to have a bath at a temperature of more than 26 degrees, it is sufficient that because the rod, for which the pipe serves as a sheath, is shorter, it has to extend farther in order for the lever to descend to the point of closing the opening of the hearth. This shortening is accomplished by the clamp at the edge of the small dial that indicates the temperature of the water in accordance with the dilation or extension of the regulator.
The inventor affirms that his furnace can keep a bath hot for four or five hours without burning a bushel of coal. To keep the feet of the sick person from touching the furnace, he has set up, three inches away from the furnace, a tin partition that only takes on the temperature of the water.
The coal fumes escape through a rubber tube led out through the chimney or out a window, but as these tubes still give off fumes that are sometimes inconvenient, we propose to replace them with copper pipes.
The application of the pyrometer to bathtubs is not only ingenious but also useful, since by using it, doctors will be certain that the sick take their baths at a temperature that will remain the same throughout the time of the bath. Your approval will assist him in perfecting the use of this measure in applying it to room stoves in order to maintain a constant temperature." Signed at the conclusion in ink by Guillotin, Lézurier, Corvisart, Le Roux des Tillets, and Adet. In fine condition.
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