By Mr. Thomas Tredgold. 581 



in full action, or boiling, and which it affords again as the 

 house cools ; a compensation taking place in this manner, 

 which renders it easy enough to proportion the quantity of 

 reservoir with as much certainty as is necessary. 



20. The ordinary method of making reservoirs and boilers 

 so large as to answer the purpose of maintaining the heat 

 during the night, has the objection already noticed of render- 

 ing it a considerable time before the apparatus can be raised 

 to a temperature capable of giving much heat ; and it appears 

 to me that it would be a material improvement to heat the 

 water for a reserve of heat, by passing the pipes of the appa- 

 ratus through the water so that its temperature should be 

 slowly raised, and the house receive heat during the time. 

 A small proportion of surface of pipe will heat the water, 

 because, water abstracts heat from a heating surface with 

 about twenty times the rapidity that air does at the same 

 temperatures ; hence, by putting a twentieth part, in addition 

 to the surface required for the house, through a proper re- 

 servoir of water it will be slowly raised to nearly the same 

 temperature as the water in the pipes, and return its heat to 

 the house as soon as the fire ceases to keep up an excess of 

 heat in the pipes. Fig. 9, shows such an arrangement where 

 c is the cistern with part of the pipe passing through it. 



21. There is very little strain on the boilers of hot water 

 apparatus, except in cases where there is much difference of 

 level ; and, as these rarely occur, consequently they may be 

 constructed in the best mode for applying heat ; which is 

 most effectively done by having as much bottom surface as 

 possible with a boiler of a given capacity. For burning a 

 bushel of coals per hour, the area of the fire grate should not 



