"I reckon you've noticed that this 'ere light seems to die away once in every forty seconds, eh?" the old man asked as he raised and lowered the cylinder. "Well, this cover of brass is what does it, an' the clock keeps it movin'. You see the clock is made fast to the brass cylinder, an' as the wheels go 'round it is raised till the whole of the flame is uncovered, an' then lowered till it's nearly shut out. The whole thing is simple enough, but it took a mighty clear-headed man to think it up. When a vessel comes off this coast, an' the cap'n sees Carys' Ledge light growin' dim an' then brightenin' up, he counts the number of seconds that go by from one bright flash to another, an' says to himself, says he: 'That 'ere is a forty-second flash, an' she's about so an' so off the coast.' Then he dives inter the cabin, hunts up his list of lights, sees which one answers to the description he's got in mind, an' says to himself, says he: 'That's Carys' Ledge, an' I'll make the course a leetle more southerly.' If that 'ere clock should happen to break down on account of not bein' properly cared for, we'd have to take turns grindin' a crank to keep the brass cylinder movin' up an' down 'cordin' to the rules an' regerlations, else there'd soon be another ship piled up on the rocks alongside the _Nautilus_." By the time Uncle Zenas had come to an end of his explanation, the necessary work had been performed, and he said with a sigh of satisfaction as he began to descend the stairs: "Now I reckon we can be gettin' at the serious part of the business! It allers makes me feel lonesome to know that the kitchen hasn't been set to rights, for that's the first place a visitor gets into when he comes to the light, an' he's liable to judge everything by what he sees there." "There isn't any great need to bother your head about visitors," Sidney said with a laugh. "People don't come out to this ledge every day." "True for you, Sonny; but s'posen the kitchen was lookin' like all possessed on that pertic'lar day? I keep it put to rights as much of the time as I can, an' then I don't stand any chance of bein' caught nappin'." Then Uncle Zenas went to work with a will, positively refusing all offers of assistance from Sidney, and, finally, the lad went into the watch-room, where he read about lenses and the refraction of light until he despaired of ever thoroughly understanding the subjects. At noon there were no signs of the keepers' return, but Uncle Zenas declared the dory would "heave in sight" within the next two hours, and proposed that they "have a bite to stay their stomachs," deferring a regular dinner until all the crew were together once more. "I don't want even a bite now," Sidney said decidedly. "Do you suppose Captain Eph would be displeased if I carried the glasses into the watch-room?" "Not a bit of it, Sonny. Use 'em wherever you please, an' I'm allowin,' if you keep a sharp lookout, you'll see the dory inside of half an hour."