GUNNERY. 291 



its end, with the fire in the bottom, and the water 1 foot thick 

 above it, with a great number of small tubes from bottom to 

 top, having' great surface sides to heat the steam above the 

 water, by working with a low chimney and slow fire, the tubes 

 in the steam part of the boiler would not exceed 600 or 700 

 of heat, which would not injure them ; as less water would be 

 generated into steam, a very small part of the boiler would be 

 sufficient for it ; and as the coal required would be less, the 

 boiler required would be very small. I state the foregoing to 

 remind you that but little is yet known of what heat may be 

 capable of performing ; as this data so far exceeds whatever 

 has been calculated on the power of heat before, when compared 

 with steam in an engine. 



" The power is sure, if we can find how to conduct it. 



" I remain, Sir, 



" Your very humble servant, 



" KICHAIJD TREVITHICK. 

 " If you can spare time please to write to me." 



The foregoing may be classed either under cannon or 

 steam-engine; Trevitliick combined them under the 

 general laws of expansion by heat. Three years had 

 passed since the committee of artillery officers sitting on 

 his gun had given a verdict of no go ; yet the subject 

 was not forgotten, and his calculations enabled him to 

 discover the explosive force, and the speed of the 

 projectile in different parts of the gun, things which are 

 now ascertained by mechanical tests and measures. 



If a 7-inch cannon 9 feet long loses by absorption of 

 heat during the time of the passage of the shot to the 

 muzzle one-half of the expansive force of the powder, it 

 is time to wrap our guns as well as our steam-engines 

 in non-conductors. The greater heat of exploded 

 powder than of steam caused eighty-eight times the 

 amount of loss from abstracted heat, and yet the force 



