Natural operations are carried on in this immense globe upon a scale which it is almost impossible for us to realize. A few illustrations gathered from Young's interesting volume, 'The Sun,' may help to make clearer to us the scale of the ruling body of our system. Some conception of the immensity of its distance from us may first be gained from Professor Mendenhall's whimsical illustration. Sensation, according to Helmholtz's experiments, travels at a rate of about 100 feet per second. If, then, an infant were born with an arm long enough to reach to the sun, and if on his birthday he were to exercise this amazing limb by putting his finger upon the solar surface, he would die in blissful ignorance of the fact that he had been burned, for the sensation of burning would take 150 years to travel along that stupendous arm. Were the sun hollowed out like a gigantic indiarubber ball and the earth placed at its centre, the enclosing shell would appear like a far distant sky to us. Our moon would have room to circle within this shell at its present distance of 240,000 miles, and there would still be room for another satellite to move in an orbit exterior to that of the moon at a further distance of more than 190,000 miles. The attractive power of this great body is no less amazing than its bulk. It has been calculated that were the attractive power which keeps our earth coursing in its orbit round the sun to cease, and to be replaced by a material bond consisting of steel wires of a thickness equal to that of the heaviest telegraph-wires, these would require to cover the whole sunward side of our globe in the proportion of nine to each square inch. The force of gravity at the solar surface is such that a man who on the earth weighs 10 stone would, if transported to the sun, weigh nearly 2 tons, and, if he remained of the same strength as on earth, would be crushed by his own weight. [Illustration: PLATE V. The Sun, February 3, 1905. Royal Observatory, Greenwich.]