The propagation of sound during fogs through pipes communicating with the shore,[43] or the origination of sound at the beacon or buoy itself, by condensing the column of air, or by acting on a column of water contained in the pipe.
Bells rung by electricity. Mr. Wilde, of Manchester, states that bells twelve or eighteen inches in diameter, placed on different beacons, and as far off as ten miles from the shore, could be tolled a hundred times a-minute by means of a three and a half or four inch electro-magnetic machine worked by an engine of about two-horse power.
And, finally, bells may be rung by the simple pressure of the waves through the agency of a float, which would sink or rise according as the tide sunk or rose. This was proposed for the beacon at the Carr Rock by the late Mr. Stevenson in 1810.
By the adoption of one or other of these suggestions, according to the conditions of the locality, there can be no doubt that the subsidiary illumination of our shores and their contiguous waters would be very considerably improved.
CHAPTER IV.
THE SKERRYVORE LIGHTHOUSE.
