4 i6 SCIENCE PROGRESS. 



lowest of these points, taking the freezing point of water as 

 8° and blood heat as 24 , and finally, about 1720, he divided 

 the degrees into fourths, the freezing point of water then 

 standing at 32° F., blood heat at 96°, and the boiling point 

 of water at 2 1 2 . The latter improvement was accompanied 

 by the replacement of spirit of wine by mercury (see Phil. 

 Trans., vol. xxxiii., p. 1, 1724). Although this appears to 

 have been the first true mercury thermometer, the use of 

 that material had been proposed as early as 1692 by Halley, 

 as already mentioned. 



In 1724 M. de l'lsle of St. Petersburg introduced a 

 system of graduation in which the boiling point of water 

 formed the zero, and the temperature of the cellars of the 

 Paris Observatory ioo°. In 1733 the same observer pre- 

 sented a paper to the Academy of Sciences of St. Peters- 

 burg (see also Phi/. Trans., vol. xxxix., p. 221, 1736), on a 

 mercurial thermometer, having its zero at the boiling point 

 of water and marked in degrees, each of which represented 

 to cm) 00 part of the total volume of mercury contained in the 

 thermometer. 



The original thermometer of Rene de Reaumur of Ro- 

 chelle, although far from delicate, was soon largely used. It 

 was introduced before 1730 (see Memoires de rAcade??iie 

 Royale de Paris, p. 645, 1730), and had a large bulb — as 

 much as three or four inches in diameter — containing a 

 known volume of spirit, the tube being so graduated that 

 each degree represented toW part of the total spirit. Ulti- 

 mately, the system of graduation was altered so that the 

 freezing point of water formed the zero and the boiling point 

 was marked at 80", the bulb being also reduced in size, but 

 the most important improvement due to Reaumur appears 

 to have been the careful expulsion of air from the spirit and 

 from the thermometer tube before sealing, a precaution 

 which had not previously been taken except in the most 

 primitive way. 



In 1740 M. du Crest introduced a spirit thermometer pro- 

 vided with the scales of Reaumur, Fahrenheit, and De l'lsle, 

 and in 1742 the valuable improvement of Anders Celsius was 

 introduced. This thermometer, which was formerly known 



