468 PHYSIOLOGICAL PHYSICS. [Chap, xxxvi. 



scales may be applied. Fahrenheit, of Dantzic, 

 introduced, in 1714, a scale in which the freezing 

 point is marked 32, and the boiling point 212 ; 32 

 below the freezing point is zero, or 0. Between 

 32 and 212 the stem is divided into 180 degrees. 

 In the Centigrade scale, introduced by Celsius, a pro- 

 fessor of Upsala, the freezing point is marked 0, and 

 the boiling point 100, and between the two 100 spaces 

 are marked off. In Reaumur's scale the boiling 

 point is 80, and the freezing point 0. The different 

 scales introduce an element of confusion. The 

 Fahrenheit is used in England ; Centigrade is becoming 

 the scale for scientific use. The reading of any one 

 scale can easily be expressed in terms of the other. 

 Nine degrees of Fahrenheit's scale = 5 of Centigrade ; 

 therefore, to express a temperature Fahrenheit in 

 terms of Centigrade subtract 32, and then multiply 



tyf 



= (F - 32) \. 



To express a temperature Centigrade in terms of 

 Fahrenheit, multiply by -, and then add 32. 



F (C x ) + 32. 



Four degrees of Reaumur's scale are equal to 5 

 Centigrade, therefore 



C == R| and E = Of. 



Nine degrees Fahrenheit = 4 Reaumur, therefore 

 F = fR-f 32, andR=(F- 32) |. 



By means of the following table approximately the 

 same temperature on the different scales may be easily 

 read. 



Alcohol is also used for thermometers, being 

 coloured to be more easily observed. Air thermo- 

 meters are also employed, and give larger indications 



