VARIOUS METHODS OF HEATING DESCRIBED IN DETAIL. 211 



Fig. 43 shows a house wherein provision is made for increas- 

 ing the heating surface, when more than a very moderate degree 

 of heat is required from the pipes. A box or tank, made of wood 

 or zinc, is placed under the stage, and passes all round it on a 

 level with the pipes. This tank is supplied by a branch pipe <z, 

 proceeding from the flow-pipe, and is provided with a tap at 3, for 

 shutting off and on the water when necessary. This is a most 

 convenient arrangement ; for, if a moderate heat only be required 

 from the apparatus, then the pipes will be sufficient, and a very 

 small fire will be required to heat them, as the quantity of water 

 is small. When it is found necessary to increase the tempera- 

 ture of the house, the pipes being then tolerably warm, the 

 water from the flow-pipe is admitted into the tank by opening 

 the tap. The heat of the pipes is slightly reduced,, but the 

 radiating surface is increased, and the temperature of the house 

 rises by an equal distribution of heat. It might be supposed 

 that a quantity of specific heat is lost to the atmosphere, by 

 drawing it from the pipes and throwing it into a body of cold 

 water. Not so, however, as a little consideration will make 

 sufficiently clear. Thus, if the atmosphere of the house be at 

 45 degrees, the water in the tank will be at 45 degrees also. 

 Now, suppose the tank and the pipes to contain equal bodies of 

 water, then, if the pipes communicate a portion of their heat to 

 the tank, the temperature of the water in the tank will rise just 

 as much as the water in the pipes will fall ; for, if two equal 

 bodies of water, at different temperatures, are mingled together, 

 the temperature produced by the mixture will be the mean of 

 their previous temperature. Suppose, for instance, that the 

 temperature of the water in the pipes was 300, and that in the 

 tank 45 degrees, and that, by the opening of the tap, the hot 

 water in the pipes, and the cold water in the tank, were inti- 

 mately mingled together, then the temperature of both would 

 be 122-5 degrees. The temperature of both has been equal- 

 ized, but the atmosphere of the house has lost none by the 

 change, but rather gained, as the tank being 77 degrees 

 above the temperature of the atmosphere, more heat will be 

 diffused than with the pipes alone at double the temperature, 

 and the object will be gained, namely, that of preventing the 



