This spell of bad weather, though in summer, well-nigh outlasted their provisions; and when at length they were able to make the signal that a landing would be practicable, scarcely twenty-four hours' stock remained on the rock. The landing of the heavy stones from the lighters was a work of no small difficulty, considering the slippery nature of the rock, and as the loss of one dressed stone would frequently have delayed the whole progress of the building, the anxiety was incessant. On July 4, the building of the tower really commenced. Six courses of masonry carried the building to the height of 8 feet 2 inches before the autumnal gales terminated the work of 1840, and an excellent year's work it was. The saying that "what is well begun is half done" was illustrated here. Next year's work was comparatively easy--so that in 1842 the tower rose to its full height of 138 feet; and the year after the light was shedding its beneficent rays over the thirty miles of watery waste that surround the hidden rocks of Skerryvore. [Illustration: The Skerryvore Lighthouse.] Well may we be proud of men like Smeaton and the Stevensons; but, while justly admiring their architectural skill, their perseverance, and their courage, we must not forget to offer the just tribute of our gratitude to the eminent natural philosophers without whose ingenious optical inventions the most splendid sea-towers would be comparatively useless. The Pharus or lighthouse of Alexandria was, probably with justice, reckoned among the seven wonders of the world, and its several stories, rising on marble columns to the height of 400 feet, must have presented an imposing spectacle, but I strongly suspect that the rude brazier on the summit of the majestic pile bore the same proportion to the lighthouse lanterns of our time as the wretched coasting-craft of the ancient Greeks to the ocean steamers of the present day. Among the names of those who have contributed most effectually to the progress of marine illumination Argand, Borda, and Fresnel are conspicuous. The hollow cylindrical wick of the first was a sudden and immense advance in the art of economical and effective illumination. The second, by his invention of the parabolic mirror, multiplied the effect of the unassisted flame by 450, and the refracting lens of Fresnel so admirably concentrates the light as to project its warning beams to the wonderful distance of thirty or thirty-five miles.