333 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



to be fulfilled ? Where is the fresh air to come from which is to 

 replace that which is taken from the room 1 by the combustion kept up 

 by the draught ? 



In olden times it was through chinks in the doors and windows 

 that this fresh supply was obtained. The fireplaces then almost 

 always smoked when these openings were properly closed, as they 

 should be in newly built houses. At all events a serious inconveni- 

 ence arose from the currents of air, which were very disagreeably 

 felt by persons sitting in the chimney corner 

 and every one knows how much draughts have 

 had to do with rheums, or rheumatic affections 

 and even in our present houses there are not 

 wanting instances where the fireplaces constructed 

 in the old way produce the same results, that is to 

 say they leave us the choice between disagreeable 

 smoke and unhealthy draughts. 



The construction of a fireplace according to 

 the requirements of science is an art which does 

 not date very far back. In the reign of Louis 

 XIV., not only in private houses, but even in 

 the palaces of the king, a poor degree of warmth 

 was maintained by making very large fires. To 

 escape the draughts they used screens, and even 

 this was not always sufficient, since Louis XIV. 

 himself in winter time used to remain in his 

 apartments snuggled up in a sort of box like 

 a carriage or sedan-chair, which prevented all 

 access of air. Besides this, as we shall see, it 

 FIG. 23i.-Draught in an W as not only the arrangement of the draught 



ordinary fireplace. 



that was defective, the utilisation of the heat 

 developed by the combustion was as bad as it could be. 



How in fact does the fire in the grate warm the room and the 

 things contained in it ? In the first place, directly by the radiation 

 from the flames and glowing coals. In the old fireplaces, therefore, 

 where the fire was at the bottom of a large square cavity bounded on 

 either side by j ambs, and above by a funnel or a shelf, all of which 

 presented obstacles to radiation, a small part only of the heat rays 

 were utilised. 



