Note 105 — MEMOIRS OF THE LIFE OF DAVID RITTENHOUSE; ANTERIOR TO HIS SETTLEMENT IN PHILADELPHIA.

It was between the years 1766 and 1770—the interval of time above mentioned,—that the two important circumstances occurred, which gave great celebrity to the reputation of Mr. Rittenhouse, as an astronomer: these were the Construction of the Orrery invented by him, and the admirable result of his observations of the Transit of Venus, as published in the Philosophical Society’s Transactions.

Amidst those objects of importance in which he was principally occupied, he occasionally amused himself with matters of minor consequence. Among other things, he contrived and made, in the beginning of the year 1767, an ingeniously contrived thermometer, constructed on the principle of the expansion and contraction of metals, by heat and cold, respectively. This instrument had, under glass, a face upon which was a graduated semi-circle: the degrees of heat and cold corresponded with those of Fahrenheit’s thermometer; and these were also correspondently designated, by an index, moving on the centre of the arch. Its square (or rather parallelogramical) form, its flatness and thinness, and its small size—together with its not being liable to the least sensible injury or irregularity, from any position in which it might be placed,—rendered it safely portable; insomuch, that it could be conveniently carried in the pocket.

He presented one of these metaline Thermometers to Dr. Peters, in June 1767: Another, which he made for himself, was a considerable time in the hands of Mr. Barton, at Lancaster. They were found to agree very well with Fahrenheit’s. In a letter to Mr. Barton, dated the 26th of July 1769, he said—“You will oblige me by sending the metaline thermometer by..., and let me know the greatest height you have seen it, this season, Fahrenheit’s thermometer, in my Observatory, not exposed to the sunshine but very open to the air, was 94½° on the 5th of this month, at 3 in the afternoon; which is the highest I have ever seen it.”