12 THE METEOROLOGY OF JAMAICA 



These were the temperature of freezing water and the tempera- 

 ture of the human body ; and it was not till afterwards that 

 the latter temperature was replaced by that of boiling water. 

 If a thermometer be placed in a tumbler containing ice and 

 water, its temperature will remain steady until all the ice is 

 melted or all the water frozen ; if the thermometer be placed 

 in an open vessel of boiling water, its temperature will again 

 remain steady until all the water is boiled away. By in- 

 creasing the fire under the open vessel the temperature of 

 the water is not increased ; it only boils away faster. The 

 boiling-point, however, varies slightly with the pressure.* 



Fahrenheit, a philosophical instrument maker of Amster- 

 dam, constructed his scale about the year 1724. He divided 

 the distance between the freezing- and boiling-points into 180 

 parts ; and he took as the zero a point 32 of these divisions 

 below the first ; so that on his scale 32 and 212 are the 

 freezing- and boiling-points respectively. 



The centigrade division of the scale was introduced by 

 Celsius, a Swede, in the year 1712. The freezing-point was 

 taken as zero, and marked 0; and the boiling-point was 

 marked 100. 



The latter scale is well adapted for the study of physics ; 

 the former is, however, more convenient for everyday require- 

 ments. When using Fahrenheit's scale we have seldom to 

 refer to negative temperatures, or temperatures below zero ; 

 and we have seldom to express temperatures in degrees and 

 tentlis ; but when scientific purposes require registration to 

 tenths of a degree, then Fahrenheit's scale again affords the 

 required accuracy. 



Fahrenheit's scale is used in English-speaking countries ; 

 the Centigrade scale is used in France, Sweden, and other 

 countries ; and Reaumur's scale is used in Germany and 

 Eussia. In the last scale the freezing-point is and the 

 boiling-point 80 ; it possesses no known advantages. 



Very accurate and comparatively cheap thermometers 

 can now be procured with the divisions etched on their stems ; 

 but still it is necessary that all such thermometers should be 

 compared with a standard thermometer at intervals of a few 

 years in order to ascertain tbeir errors. 



* It is 212 when the pressure is 29 938 (stand, grav.). 



