Civilisation : Its Cause and Cure 



remainder of the sentence will help us. ** The 

 temperature is 30° Fahrenheit." ** The unknown 

 thing is thirty degrees." What then is a degree ? 

 That is the next question. When the Theory of 

 Heat went out from sensation and left it behind, 

 one of its first landing places was in the expansion 

 of liquids — as in thermometer tubes. Here for 

 some time was thought to be a satisfactory register 

 of " temperature." But before long it became 

 apparent that the degree — Fahrenheit, Reaumur, 

 or what-not — was an entirely arbitrary thing, 

 also that it was not the same ^ thing at one end 

 of the scale as the other, and finally that the scale 

 itself had no starting point ! This was awkward, 

 so a move was made to the air thermometer, and 

 there was some talk about an absolute zero and 

 absolute temperatures ; it was thought that the 

 Unknown thing showed itself most clearly and 

 simply in the expansion of air and other gases, 

 and that the " degree " might fiirly be measured 

 in terms of this expansion. But in a little time 

 this kind of thermometer — chiefly because no 

 gas turned out to be " theoretically perfect " — 

 broke down, absolute zero and all, and another 

 step had to be made — namely, to the dynamical 

 theory. It was announced that the Unknown 

 thing might be measured in terms of mechanical 

 energy, and Joule at Manchester proclaimed that 



* The very fact alone that the degrees on a thermometer are 

 ffua/ space divisions shows that they must bear a varying relation 

 to the total volume of liquid as that expands from one end of the 

 tube to the other. 



I 12 



