CONDUCTION AND RADIATION. 



the true law for radiation, and by other writers for 

 conduction. This assumption was confirmed ap- 

 proximately, and afterwards corrected, for the case 

 of radiation ; in its application to conduction, it 

 has been made the basis of calculation up to the 

 present time. We may observe that this statement 

 takes for granted that we have attained to a mea- 

 sure of heat (or of temperature, as heat thus 

 measured is termed,) corresponding to the law thus 

 assumed ; and, in fact, as we shall have occasion to 

 explain in speaking of the measures of sensible qua- 

 lities, the thermometrical scale of heat according 

 to the expansion of liquids, (which is the measure 

 of temperature here adopted,) was constructed with 

 a reference to Newton's law of radiation of heat ; 

 and thus the law is necessarily consistent with the 

 scale. 



In any case in which the parts of a body are 

 unequally hot, the temperature will vary continu- 

 ously in passing from one part of the body to 

 another ; thus, a long bar of iron, of which one end 

 is kept red hot, will exhibit a gradual diminution 

 of temperature at successive points, proceeding to 

 the other end. The law of temperature of the 

 parts of such a bar might be expressed by the 

 ordinates of a curve which should run alongside 

 the bar. And, in order to trace mathematically 

 the consequences of the assumed law, some of 

 those processes would be necessary, by which ma- 

 thematicians are enabled to deal with the proper- 



