Fahrenheit made his thermometers with different scales at different times, commonly known as the large, medium, and small scales, their correspondence and value being shown in the table.
| I. Large. |
II. Medium |
III. Small. |
(Centigrade.) |
|---|---|---|---|
| 90 | 24 | 96 | 35.5 |
| 0 | 12 | 48 | 8.8 |
| −90 | 0 | 0 | −17.8 |
In No. I the 0° was placed at "temperate" as in the Florentine scale; in No. II each space was divided into four equal parts, and these smaller divisions were afterwards taken as degrees, thus forming scale No. III.
The earliest thermometers were made to indicate temperature up to 96° only; it does not appear that Fahrenheit used the boiling-point of water as a fixed point, although he alludes in his first paper to the fact that Amontons had shown that water boils at a constant temperature. The origin of the numbers 32 for the freezing-point and 212 for the boiling-point of water is obscure, they may have arisen in this way: After Fahrenheit abandoned the Florentine scale −90–0–90, he arbitrarily contrived the scale o–12–24 taken from the familiar foot measure, but the spaces being too
