Temperature. Thermometers 147 



and boiling points is 180. The freezing-point is 

 marked 32 and the boiling-point 212. This scale is 

 due to Fahrenheit, and thermometers thus marked are 

 called by his name. The graduations are usually con- 

 tinued above and below the fixed points to an extent 

 which depends upon the purpose for which the ther- 

 mometer is intended. In all scientific work a scale 

 in which the freezing-point is marked and the 

 boiling-point 100 is used. This is the Celsius, or, as 

 it is more commonly termed, the Centigrade, scale. 

 A third method of graduation, due to Reaumur, is in 

 common use on the Continent, more especially in the 

 northern countries. In this the freezing-point is 

 marked and the boiling-point 80. 



Temperatures below zero on any scale are expressed 

 by counting the number of degrees from the zero mark 

 in the opposite direction to that in which temperatures 

 above zero are counted, such low temperatures being 

 distinguished by prefixing the minus sign. Thus a 

 temperature of 10 below the zero of the Centigrade 

 scale would be written 10 C. 



Temperatures expressed according to any one of 

 these methods may be changed into their corresponding 

 values on either of the other scales by noting that 



80 Reaumur = 100 Centigrade = 180 Fahrenheit, 



and that, in changing degrees Fahrenheit into either 

 Reaumur or Centigrade readings, 32 must be first 

 subtracted from the Fahrenheit value, while, in effecting 

 the reverse change, 32 must be added to the value 

 obtained. 



Example : Transform 85 C. into degrees F., and 

 15 F. into degrees R. 



(a) 85 C. = (85 x {fg) F. = 153 F. 



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