2 EXPANSION OF SOLIDS. 



1. Expansion, the most general effect of heat, and the Ther- 

 mometer. 



2. Specific Heat. 



3. The communication of heat by Conduction and Radiation. 



4. Liquefaction, as an effect of heat. 



5. Vaporization, or the gaseous state, as an effect of heat. 



6. Speculative notions which have been entertained respecting 

 the Nature of heat. 



EXPANSION AND THE THERMOMETER. 



All bodies in nature, solids, liquids, or gases, suffer a tempo- 

 rary increase of dimension when heated, and contract again into 

 their original volume on cooling. 



1. Expansion of solids. The expansion of solid bodies, such 

 as the metals, is by no means considerable, but may readily be 

 made sensible. A bar of iron, which fits easily when cold into 

 a gauge, will be found, on heating it to redness, to have in- 

 creased sensibly both in length and thickness. The expansion 

 and contraction ol metals, indeed, and the immense force with 

 which these changes take place, are matters of familiar observa- 

 tion, and are often made available in the arts. The iron hoops 

 of carriage wheels, for instance, are applied to the frame while 

 they are red hot, and in a state of expansion, and being then 

 suddenly cooled by dashing water upon them, they contract 

 and bind the wood work of the wheel with great force. The 

 expansion of solids, however, is very small, and requires nice 

 measurement to ascertain its amount. The expansion in length 

 only has generally been determined, but it must always be re- 

 membered that the body expands also in its other dimensions, 

 in an equal proportion. The first general fact observable is, that 

 the amount of dilatation by heat is different in different bodies. 

 No two solids expand alike. The metals expand most, and their 

 rates of expansion are best known. Rods of the undermen- 

 tioned substances, on being heated from the freezing to the 

 boiling point of water, elongate as follows : 



Lead ... 1 on 351 Pure Gold . 1 on 682 



Silver ... 1 524 Iron Wire . 1 812 



Copper ... 1 581 Platinum . . 1 1167 



Brass 1 584 Flint Glass 1 1248 



