Denmark. For eighteen years Fahrenheit kept secret his method of manufacture for commercial reasons, but between 1724 and 1726 he published five brief papers in the Philosophical Transactions. Many of the experiments date, however, from 1721.
In the first of these he gives the specific gravity and boiling-points of five liquids, alcohol, rain-water, nitric acid, potash-lye, and sulfuric acid, taken at 48° of his scale; this temperature, he explains, is half-way between that of the intense cold obtained by a mixture of water, ice and sal-ammoniac, or common salt, and that of the blood of man.
The second paper, on the freezing of water in vacuo, contains the interesting observation that water can remain liquid below its freezing-point; incidentally Fahrenheit describes his thermometer.
The third paper contains the specific gravity of 29 substances, solid and liquid, the determination having been made with the balance and with the new hydrometer described in paper No. 4. This instrument was the first hydrometer of constant volume; it had a pan for carrying weights like Nicholson's (which
