CHAP, in.] ON THE CONDUCTIBILITY OF HEAT. 357 



CHAPTER III. 



VAIUOUS APPLICATIONS OF THE LAWS OF THE CONDUCTIBILITY OF 



HEAT. 



I. DWELLINGS. 



THE temperature of an apartment depends not only upon the heat- 

 ing apparatus which are placed in it, or on the heat which these 

 may communicate to the air by way of radiation or convection, or 

 any other mode of propagation ; but it depends also, in the first place, 

 on the temperature outside, and, in the second place, on the greater 

 or less efficacy with which the walls or other protections oppose the 

 passage of the heat from within outwards. This inevitable loss is 

 more or less rapid according (1) to the thickness of the walls, or (2) 

 according to the materials of which they are made, such as wood or 

 other bad conductors of heat, or (3) according as the openings in 

 them, closed only by glazed windows so as to admit the daylight, 

 are more or less numerous, and present a greater or less surface. 



Thick walls, made of materials which are bad conductors, have 

 the double advantage of protecting the inmates in winter against 

 the cold, and in summer against the heat. Stone and marble are in 

 this respect less advantageous than brick, and much less than wood. 

 In cold countries, as in Russia for instance, many of the country 

 houses have their walls made of beams or thick planks, forming a 

 double partition which is filled with broken materials, chopped straw, 

 sawdust or dried moss. The air which is entangled in the interstices 

 of this loose material forms with the partitions a combination very 

 impermeable to heat, and a very bad conductor, and consequently 

 an excellent protection against the low temperature of the outside. 



But it is through the doors and glazed windows that in the day- 



