THE AIR OF STOVE-HEATED KOOMS. 57 



on to say that the open fireplace " gives heat only by heating 

 the walls, ceiling, and furniture ; and here is the great advan- 

 tage of the open fire ;" and, further, that " if the air in the 

 room were hotter than the walls, condensation would take 

 place on them, and mildew and fermentation of various kinds 

 would be engendered ; whereas, if the air were cooler than the 

 walls, the latter must be absolutely dry." 



Upon these assumptions, Dr. Siemens condemns steam 

 pipes and stoves, hot-air pipes, and all other methods of 

 directly heating the air of apartments, and thereby making it 

 warmer than were the walls-, the ceiling, and furniture when 

 the process of warming commenced. It is quite true that 

 stoves, stove-pipes, hot-air pipes, steam pipes, etc. do this : 

 they raise the temperature of the air directly by convection 

 i.e. by warming the film of air in contact with their surfaces, 

 which film, thus heated and expanded, rises toward the ceil- 

 ing, and, on its way. warms the air around it, and then is 

 followed by other similarly heated ascending films. When we 

 make a hole in the wall, and burn our coals within such cavity, 

 this convection proceeds up the chimney in company with the 

 smoke. 



But is Dr. Siemens right in saying that the air of a room, 

 raised by convection above its original temperature, and above 

 that of the walls, deposits any of its moisture on these walls ? 

 I have no hesitation in saying very positively that he is clearly 

 and demonstrably wrong ; that no such condensation can possi- 

 bly take place under the circumstances. 



Suppose, for illustration sake, that we start with a room of 

 which the air and walls are at the freezing point, 32 Fain 1 ., 

 before artificial heating (any other temperature will do), and, 

 to give Dr. Siemens every advantage, we will further suppose 

 that the air is fully saturated with aqueous vapor i.e. just in 

 the condition at which some of its water might be condensed. 

 Such condensation, however, can only take place by cooling 

 the air below 32, and unless the walls or ceiling or furniture 

 are capable of doing this they cannot receive any moisture due 

 to such condensation, or, in other words, they must fall below 

 32 in order to obtain it by cooling the film in contact with 

 them. Of course Dr. Siemens will not assert that the stoves 

 or steam-pipes (inclosing the steam, of course), or the hot-air 

 or hot-water pipes, will lower the absolute temperature of the 

 walls by heating the air in the room. 



But if the air is heated more rapidly than are the walls, etc. 



