198 Domestic Science 



question whether the correspondingly greater radiating 

 power does not almost entirely compensate for the 

 advantage of ready absorption. The white flannel of 

 the cricketer reflects heat better than would a darker 

 material, but, on the other hand, the heat received 

 from the body is not absorbed as readily. It is probably 

 rather a matter of convenience which decides the colour 

 of our clothes than the conscious application of experi- 

 ence, and dark materials find more favour in winter 

 on account of the great labour which would be involved 

 in keeping light garments clean in such a climate as 

 ours during the cold season. 



132. The chief points dealt with in this chapter 

 may be briefly summarised as follows : 



Solid bodies transmit heat by conduction alone, the 

 heat received by the molecules nearest the source of 

 heat being passed on to those next them, these latter 

 passing on their heat in turn, and the continued repe- 

 tition of this process resulting in the propagation of 

 the heat in all directions through the solid. 



Liquids and gases transmit heat chiefly by con- 

 vection, actual motion of the heated part of the fluid 

 taking place away from the heating agent to cooler 

 regions and other parts of the fluid moving towards 

 the neighbourhood of the source of heat, to be heated 

 and move away in their turn. 



Through space and also to a very large extent 

 through gaseous media, heat is propagated by the 

 setting up of wave motion of a certain magnitude, the 

 medium being unchanged in temperature by the 

 passage of the heat, and the latter only becoming 

 sensible when the waves meet an object, when the 

 energy transmitted by them is transformed into that 

 form of energy which we call heat. 



