Sir John Herschel found that the heating power of the sun when it was directly overhead was capable of melting .00754 of an inch of ice per minute. According to M. Pouillet the quantity was .00703 of an inch, which is equal to about half-an-inch per hour. From these results it has been calculated that if the direct heat of the sun were received upon a block of ice one mile square, 26,000 tons would be melted per hour by the heat which would be absorbed. Again, as Herschel[12] puts it: "Supposing a cylinder of ice, 45 miles in diameter, to be continually darted into the sun with the velocity of light, the heat given off constantly from the sun by radiation would be wholly expended in liquefaction on the one hand, while on the other, the actual temperature at the sun's surface would undergo no diminution." Sir John Herschel further says: "All the heat we enjoy comes from the sun. Imagine the heat we should have to endure if the sun were to approach us, or we the sun, to a point the one hundred and sixtieth part of the present distance. It would not be merely as if 160 suns were shining on us all at once, but 160 times 160 suns according to the rule of inverse squares--that is, 25,600. Imagine a globe emitting heat 25,600 times fiercer than that of an equatorial sunshine at noonday, with the sun vertical. In such a heat there is no solid substance we know of which would not run like water, boil, or be converted into smoke or vapour." Lockyer points out that the heat radiated from every square yard of the sun's surface is equal to the amount of heat produced by the burning of six tons of coal on that area in one hour. Now the surface of the sun may be estimated at 2,284,000,000,000 square miles, and there are 3,097,600 square yards in each square mile; what therefore must be the number of tons of coal which must be burnt per hour to represent the amount of heat radiated from the sun into space? The approximate result may be calculated by multiplication, but the figures arrived at fail to give any adequate conception of the actual result.