- trast the reasoning of Mr. Alan Stevenson, the builder of the "Skerryvore,"
another of these deep-sea lamp-posts, as they have been called, off the western coast of Scotland,—with the instincts of Smeaton, so to speak, on the same subject. It may not be very edifying to the general reader to learn "that, as the stability of a sea-tower depends, cæteris paribus, on the lowness of its centre of gravity, the general notion of its form is that of a cone; but that, as the forces to which its several horizontal sections are opposed decrease towards its top in a rapid ratio, the solid should be generated by the revolution of some curve line convex to the axis of the tower, and gradually approaching to parallelism with it; and that this, in fact, is a general description of the Eddystone Tower, devised by Smeaton." Neither is it a thing likely to be remembered, without saying it over a good many times to oneself, that "the shaft of the Skerryvore pillar is a solid, generated by the revolution of a rectangular hyperbola about its asymptote as a vertical axis." But if we understand the respective narratives of the constructors rightly, Smeaton worked from analogy, and Stevenson from mathematical calculation. Smeaton tells us of his desire to make his lighthouse resemble the trunk of a stately tree, and he gives drawings both of a trunk and of a branch, to show how they start, the one from the ground, and the other from the main stem. He is also constantly recurring to the idea of the elasticity of stone, and he quotes a report from one of the keepers, that on one occasion "the house did shake as if a man had been up in a great tree." Certainly, the effect to the eye in looking at the Eddystone, corroborates the conception with which his mind was evidently possessed; it emerges from the sea; the curve of the natural rock is continued in a singularly felicitous manner; the Skerryvore is a fine shaft, but one sees that it has been stuck in a hole, thoroughly well fastened in, and (relying on its weight and coherence) likely to remain there till doomsday; but the Eddystone is homogeneous to the rock, as well as to itself; and gazing on it, one gets into the same train of contemplation as Topsy did upon her wickedness, and supposes it grew there. Nevertheless the Skerryvore is a noble structure, and the memoir of its construction by Mr. Stevenson is almost exhaustive of all that is at present known about lighthouses and lighthouse illumination.
And if these be the lighthouses, and the mode of life among those by whom they are builded, let us try to realize the daily work of those by whom the structures are inhabited. "You are to light the lamps every evening at sun-setting, and keep them constantly burning, bright and clear, till sun-rising." That is the first article of instructions to light-keepers, as may be seen by any visitors to a station. Whatever else happens, you are to do that. It may be you are isolated, through the long night-watches, twenty miles from land, fifty or a hundred feet above the level of the sea, with the winds and waves howling round you, and the sea-birds dashing themselves to death against the gleaming lantern, like giant-moths against a candle; or it may be a calm, voluptuous, moonlight night, the soft land-
