The execution of steam-engines has had, like that of all other machines, its different epochs, to which successively corresponded new degrees of perfection. To diminish, as far as possible, the quantity of vaporisation requisite for the effect in contemplation, and to make a moderate use of the combustible; to combine with this chief economy that of substance and of workmanship, by contracting the dimensions of the pieces without diminishing their utility; to prevent explosions, by the wisest precautions adopted in the management of an agent whose power becomes destructive when it is not limited: these are in general the objects which have fixed the attention of engineers, and have excited among them a laudable kind of rivalship.[94] In no invention, either for ingenuity or utility, has modern genius been more conspicuous than in the invention of the steam-engine. The amazing power wielded by man, by this means, is just matter of astonishment and wonder. In no part of the kingdom have these stupendous machines been brought to greater perfection, either in size or principle, than in the mining counties of Cornwall and Devon. The largest ever built has lately been erected at Chacewater mine, in the county of Cornwall, by Mr. S. Moyle, of that place, and is for size and efficiency, as well as neatness, without a parallel. This stupendous machine is equal to 1,010 horses; it works day and night in pumping dry a mine of 100 fathoms deep, and of a large extent: and the quantity of water pumped out in one minute, and the column consequently lifted, is greater than any other machine of the kind ever erected. The whole reflects the greatest credit on the abilities of the engineer, and forms an interesting object to all those who are curious in mechanism, or who may visit the mines of Cornwall.[95] A very ingenious naturalist suggests the idea, that subterraneous fire, and steam generated from it, are the true and real causes of earthquakes. And he thinks the elasticity of steam and its expansive force, are every way capable of producing the stupendous effects attributed to earthquakes, when it is considered that this expansive force of steam is to that of gunpowder as 140 to 5. He also apprehends that subterraneous fire must, at different times, have existed universally in the bowels of the earth, and that in union with water, or by the expansive power of steam, it has produced the immense continents, as well as the mountains of our globe.[96] There are, in the Memoirs of the Paris Academy of Sciences for the year 1707, some observations communicated by Vauban, from which it results that 140 pounds of water converted into vapor, would produce an explosion capable of blowing up a mass of 77,000 pounds, while 140 pounds of powder could only produce a similar effect upon a mass of 30,000.