THERMOMETER AND PYROMETER. 







J. De Lisle of St. Petersburg, differs 

 little in principle from the instruments 

 just mentioned ; but its graduation is 

 inverted. His is at the'boiling point 

 of water, and he continues the gradua- 

 tion dwcnirards: and conceiving the 

 mercury, at that temperature, to be di- 

 vided into 100,000 parts, he determined 

 the degrees by the contractions of the 

 whole mercury as it cooled, expressed 

 in such parts.* The distance between 

 the freezing and boiling points of water 

 on this scale is 150, as ascertained by 

 Dr. Martine, who examined one of Dr. 

 Lisle's original thermometers : but this 

 thermometer seems to possess no advan- 

 tage over those just described, and never 

 came into general use except in Russia, 

 where it is still employed. 



Our countryman, Dr. Stephen Hales, 

 employed another thermometer in his 

 experiments on vegetable physiology. 

 The was at freezing water, and the 

 highest point was ascertained by placing 

 the instrument in hot water, on ^ which 

 wax was just beginning to congeal ; 

 the intervening space was divided into 

 100.t This near approach to a true 

 centesimal scale was defeated by the un- 

 certainty of the upper point, arising 

 from his using spirit instead of mercury 

 in the tube, and the difficulty of ascer- 

 taining the exact moment of the conge- 

 lation'of the wax. 



In the year 1742, the Swedish philo- 

 sopher Celsius, professor at Upsal, 

 divided centesimalty the thermometer 

 known in the north by his name, and 

 which has, since its tacit adoption by 

 the French chemists, obtained additional 

 celebrity as the ThermomHre Centi- 

 grade. Celsius commences his scale 

 at the freezing point of water, and di- 

 vides the space between that point and 

 the height of the mercurial column in 

 boiling water into 100. This appears 

 a more natural and simple division than 

 any that had been previously proposed, 

 and it possesses several advantages ; 

 but it has two inconveniences of some 

 importance in many practical opera- 

 tions. Thus, from the high position of 

 the 0, natural colds are frequently to 

 be noted by a descending series of fi- 

 gures, and one column of observations 

 may be hence embarrassed by + and 

 degrees ; while from the large space 

 intercepted between the degrees, the 

 observer is frequently obliged to com- 

 pute fractional parts of a degree. 



* Phil. Trans, vol. xxxix. p. 221, for 1736. 

 t Vegetable ritatics, vol. i. p. 5^. 



M. de la Lande, in 1804, proposed a 

 new thermometric scale, the or mean 

 point of which he would fix at the mean 

 temperature of the earth ; which he 

 gives as = to 9. 5 of Reaumur's scale ; 

 and his degrees were to be the ten mil- 

 lionth part of the volume of the mer- 

 cury in the instrument. Among the 

 advantages of such a division, he con- 

 siders the simplification of expression in 

 meteorological observations thus, 30 

 would express the heat of summer and 

 cold of winter ; 40 a hot summer and 

 severe winter; while the smallness of 

 the degrees would obviate the use of 

 fractions of a degree. The boiling 

 point of water would be at + 133, 

 and the congelation of mercury at 

 74 ; ice would melt at 1 8, and the 

 zero of Fahrenheit would be at 44.* 



This proposition has never been 

 adopted ; and its advantages seem over- 

 rated by the inventor. It only obviates 

 one of the objections urged against the 

 scale of Celsius, and is inferior in sim- 

 plicity either to a millesimal division of 

 the interval between the freezing and 

 boiling point of water, or to the ther- 

 mometric scale proposed by the late 

 Dr. Murray of Edinburgh. That acute 

 philosopher proposed to employ the 

 freezing and boiling points of mercury 

 itself as the extremes of his scale, and 

 to divide the intervening space into 

 1000. It is a more natural division 

 than any hitherto proposed, inasmuch 

 as it is taken from relations of the best 

 thermometric fluid itself to heat : and if 

 we suppose these two points to have 

 been accurately fixed at 40 and -r- 

 655 of Fahrenheit, the freezing point of 

 water would be 99, and its boiling 

 point 347 on Murray's scale. 



The advantages of this scale, are that 

 it will very seldom, in natural tempera- 

 tures, render the introduction of de- 

 grees necessary, and the smallness of 

 the divisions supersede the employment 

 of fractional parts of a degree, in ordi- 

 nary cases ; two circumstances of con- 

 siderable importance in a long series of 

 thermometric observations. 



Magellan informs us, f that M. 

 Achard of Berlin invented a thermome- 

 ter for ascertaining high temperature, 

 which is a true Pyrometer, and might 

 have been introduced in the next sec- 

 tion. It consists of a ball and tube of 

 semitranslucent porcelain, highly baked, 



Journal de Physique, 1804. Nicholson's Jour- 

 nal, 8vo. vol. ii. p. 61. 

 t Snr la Tbeorie du Feu Ele"mentaire, 1780, 



