The Carr rock is about six miles north-north-east of the Isle of May lighthouse, and twelve miles south-west of the Bell Rock.
In a recent pamphlet,[42] Mr. Thomas Stevenson, the engineer to the Board of Northern Lights—who has an hereditary as well as an individual claim to be heard on all matters of this kind—has suggested various modes of lighting beacons and buoys. As he observes, the importance of raising them to the rank of illuminated night-marks must be apparent to all who know anything of coast navigation; and he is certainly justified in thinking that the subject is worthy of more attention than has hitherto been given to it.
He speaks, in the first place, of apparent or borrowed lights, where a ray is thrown on a buoy or beacon—as in the case of the Arnish Rock, referred to on page 274,—from a neighbouring lighthouse. The only other existing example of an apparent light is to be found at the harbour of Odessa, in the Black Sea. It was constructed in 1866, and is situated three hundred feet from the shore.
Mr. Stevenson’s next suggestion applies to dipping lights for sunk rocks, where it would be difficult or impossible to erect a beacon for containing the necessary optical apparatus. Here he would so arrange the lamp and reflectors of the lighthouse as to dip vertically, and thus project a cone of rays upon the sea for a considerable area round the secret danger. On seeing the illuminated wave-space the mariner would alter his course, and give the sunken rock a “wide berth.”
The other methods proposed by Mr. Stevenson are:—
The conduction either of voltaic, magnetic, or frictional electricity, singly or combined, to the buoy or beacon, through wires, submarine, or, where practicable, suspended in the air, so as to produce a spark either with or without vacuum tubes, or by means of an electro-magnet and the deflagration of mercury.
The conduction of gas from the shore in submarine pipes.
Self-acting electrical apparatus, produced by the action of sea-water or otherwise at the beacon itself, so as to require no connection with the shore.
And, finally, Mr. Stevenson recommends different applications of sound, so as to produce distinct and powerfully audible warnings during the prevalence of a thick fog or mist:—