lbs. 1 lb. of carbon in powder 3,548,160 } 14 times the consumption 1 lb. of coal in Boulton and Watt's } engine 240,000 } by the engine. 1 foot of cold sides of the gun 221,760 { 88 times as much loss 1 " " of the cylinder 33,750 { by the cold sides of { the gun 1 lb. of coal for 7 lbs. of water in { 14 times as much coal steam { for water into steam 1 lb. of carbon for 8 oz. of water in powder { as for water in powder { powder. "By this it appears that heat is loaded with fourteen times as much water in steam-engines as in powder, and does only 1/14th part of the duty of the water in powder. It is possible to heat steam independent of water, because if we work with steam of ten atmospheres, it would have ten times the capacity for heat, being in proportion to its gravity. The boiler standing on 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, "RICHARD TREVITHICK. "If you can spare time please to write to me." The foregoing may be classed either under cannon or steam-engine; TREVITHICK 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.