With such advantages, it may be asked: Why does not the gas-engine everywhere supersede the steam-engine? My answer is a simple one: The gas we manufacture is a dear fuel compared with coal. Ordinary coal gas measures 30 cubic feet to the pound; and 1,000 cubic feet, therefore, weigh 33 lb. Taking the price at 2s. 9d. per 1,000 cubic feet, it costs 1d. per lb. The 30 cubic feet at 630[theta] give 19,000[theta] all available heat. Although good coal may yield 14,000 units by its combustion, only about 11,000 of these reach the boiler; so that the ratio of the useful heat is 11/19. The thermal efficiency of the best non-condensing engine to that of the gas-engine is in the ratio 4/22. Multiplying together these two ratios, we get 11 4 44 -- x ------- = ---- 19 22_{1/2} 4.28 That is, speaking roughly, 1 lb. of gas gives about ten times as much power as 1 lb. of coal does in a good non-condensing engine. But at 18s. 8d. a ton we get 10 lb. of coal for 1d.; so that with these figures the cheapness of the coal would just compensate for the efficiency of the gas. As to the waste heat passing away from the engine being utilized, here the gas-engine has no advantage; and, so far as this is concerned, the gas is about eight times dearer than coal. The prices of gas and coal vary so much in different places that it is hard to determine in what cases gas or coal will be the dearer fuel, considering this point alone. But there are other kinds of non-illuminating gases--such as Wilson's, Strong's, and Dowson's--which are now coming into use; and at Messrs. Crossley's works you will have an opportunity of seeing a large engineering factory employing several hundred mechanics, and without a chimney, in which every shaft and tool is driven by gas-engines supplied by Dowson's gas, and in which the consumption of coal is only 1.2 lb. per indicated horse power. The greatest economy ever claimed for the steam-engine was a consumption of 1.6 lb.; and this with steam of very high pressure, expanded in three cylinders successively. Thus in a quarter of a century the gas-engine has beaten in the race the steam-engine; although from Watt's first idea of improvement, nearly a century and a quarter have elapsed.