VARIOUS INVKNTIONS. 11 



extremely well, but it is impossible for him to settle anything 

 apart from the adventurers. 



" I am very sorry that anyone should have executed the plan 

 of reducing copper ore by a blast-furnace before you had put 

 into practice the idea suggested to me ten years ago. It ascer- 

 tains, however, that the contrivance will succeed, although you 

 are certainly reduced to ask moderate terms, and I know not 

 what can be more moderate than those you have asked, except 

 that I would recommend some limit as to time. 



" The plan you suggest for an engine on a new construction 

 is, I fear, very doubtful. 



" According to the data furnished to me, the air in the blast 

 would be to that in a common fire-place as 6J to 1 very nearly, 

 provided their densities were the same ; but you have measured 

 one entering the furnace at the common temperature, and the 

 other going to the stack so hot as to set on fire a piece of paper 

 held at the top. Thus the increase of temperature that augments 

 the elasticity of a fluid confined, would expand it in the same 

 degree. It is therefore uncertain from these statements which 

 furnace consumes the greater quantity of air. I apprehend the 

 general principles of an engine worked by hot air, through the 

 medium of a blast, would be as follows : 



" Let any quantity of air be driven into a furnace with the 

 pressure of an atmosphere, and let it be there expanded ten 

 times. It should then be taken off ten times as quick, but in 

 that case no power whatever would be produced, so the external 

 atmosphere would balance the internal. Now, let the blast be 

 two 'atmospheres strong, and let them be expanded ten times, 

 and be taken off ten times as fast, each stroke will be opposed 

 by one, equal in all to ten ; subtract two for the blast, there 

 remain eight. 



" But air so hot would burn every vegetable or animal sub- 

 stance, and such a furnace I suppose could scarcely be kept air- 

 tight. If the heated air is made to act on water, then it becomes 

 a mere question of how much absolute heat is given out by the 

 fuel, and whether that excess is more than sufficient to com- 

 pensate the burden of the blast ; for the water will absorb an 

 immense quantity of heat in changing itself into steam, and 



