Page:Evolution of the thermometer.djvu/63

 inches down in inches and lines (pouces and lignes), so that on this scale 51.5 inches were equal to 0° C., and 73 inches to 100° C. Readings were corrected by a barometer. This instrument registered the changes in the elastic force of air produced by heat, and was styled by Amontons the "universal thermometer;" but its great length, the difficulty of transporting it, and the inaccuracy due to friction of mercury in the glass tube, prevented it from being adopted.

Amontons is often credited, especially by French authors, with the discovery that the boiling-point of water is constant under like conditions as respects pressure, etc., but this cannot be sustained for it is certain that Renaldini anticipated him in proposing the boiling-point of water as a fixed point, and that Boyle and Papin demonstrated the influence of pressure long before.

The French physicist constructed a mercury thermometer provided with a double scale ascending from 49 to 59 and descending from 14 to 24; in this were the following correspondences: 59° = solidification of tallow ; 54° = cellars of the observatory, Paris; 52° = freezing of water. This instrument had no advantages over those in use.