Thermometric Scales for Meteorological use 423 



his life there, he considered that the greatest winter cold 

 which he had experienced in that rigorous climate might, for 

 all the purposes of human life, be accepted as the greatest 

 cold which required to be taken into account. He found 

 that this temperature could be reproduced by a certain 

 mixture of snow and salt. As a higher limit of temperature 

 which on similar grounds he held to be the highest that was 

 humanly important, he took the temperature of the healthy 

 human body, and he subdivided the interval into twenty-four 

 degrees, of which eight, or one-third of the scale, were to 

 be below the melting-point of pure ice, and two-thirds or 

 sixteen were to be above it. Fahrenheit very early adopted 

 the melting temperature of pure ice for fixing a definite point 

 on his thermometer, but he recognised no right in that tem- 

 perature to be called by one numeral more than by another. 

 The length of his degree was one-sixteenth of the thermo- 

 metric distance between the temperature of melting ice and 

 that of the human body, and the zero of his scale was eight 

 of these degrees below the temperature of melting ice, and 

 not as is often thought, the temperature of a mixture of ice 

 and common salt or sal-ammoniac. Fahrenheit, as has been 

 said, was the first to use mercury for filling thermometers ; 

 and being a very skilful worker, he was able to make ther- 

 mometers of considerable sensitiveness, on which his degree 

 occupied too great a length to be conveniently or accurately 

 subdivided by the eye. To remedy this he divided the length 

 of his degree by four, and the temperature from the greatest 

 cold to the greatest heat which were of importance to human 

 life came to be subdivided into 96 degrees. 



Had he lived in the following century he would have been 

 able to point out that on his scale the range of temperature 

 within which human beings find continued existence possible 

 is represented by the interval o to 100 degrees, and there 

 can be little doubt that this would have secured its general 

 adoption. Its preferential title to the name Centigrade 

 is indisputable. Perhaps this may be an assistance to its 

 rehabilitation as the thermometer of meteorology 1 . 

 1 See Contents, p. xxxiii. 



