90 ELEMENTS OF SCIENCE 



water is 32 and its boiling point 32 + 180, or 212". 

 The lowest point of this scale is called " zero," and de- 

 grees below this, are spoken of as so many degrees below 

 zero. The degrees between zero and 32 are also spoken 

 of as so many " degrees of frost." Thus 20 marks 

 twelve degrees of frost. On the Continent, Centigrade 

 thermometers are used, according to which the space 

 between the points of freezing and boiling water is 

 divided into 100 degrees, and the freezing point is the 

 zero of that system. 



Now if various bodies of different kinds, all have their 

 temperature simultaneously changed to the same extent 

 (all made 10 hotter or colder) fchey will expand differ- 

 ently ; that is, the ratio of the change of bulk will be 

 different for every different substance. 



Different substances have, indeed, very different 

 capacities for heat, and the same amount of heat, com- 

 municated to two different bodies whose masses or weights 

 are equal, will not cause the same rise of temperature in 

 each. Thus a pound of water at 40 and a pound of mer- 

 cury at 1 60, if mingled together, will not produce a mass 

 of a temperature of 100, but only one of 45, the tempera- 

 ture of the water thus having only risen 5, while that 

 of the mercury has fallen 115% 



If we take equal masses of different bodies, A, B, C, 

 D, &c., then the numbers which are proportional to the 

 various amounts of heat required to make them all of 

 the same temperature are called the specific heats, or the 

 capacities for heat, of A, B, C, D, &c., respectively. 



But, as before said, heat not only expands bodies, but, 

 if continued, will change solids into liquids and liquids 

 into gases. Sometimes, but by no means always, solids 

 will, in melting, pass through an intermediate, or jelly- 

 like, condition before becoming liquid. A jelly is a sub- 



