TRANSACTIONS OF THE SECTIONS. 217 
bear up the weight of the wirealone. Thus it results that the arrival of the sinker 
at the bottom is indicated very exactly on board the ship by the sudden cessation 
of the revolving motion of the drum from which the wire was unrolling. 
Another novel feature of great importance consists in the introduction of an addi- 
tional hauling-up drum or pulley, arranged to act as an auxiliary to the main drum 
during the hauling-up process. The auxiliary drum has the wire passed once or 
twice round its circumference at the time of hauling up, and is turned by men so 
as to give to the wire extending from it into the sea most of the pull requisite for 
drawing it up out of the sea, and it passes the wire forward to the main drum, there 
to be rolled in coils relieved from the severe pull of the wire and sinker hanging in 
the water. Thus the main drum is saved from being crushed or crumpled by the 
excessive inward pressure which would result from two or three thousand coils of 
very tight wire, if that drum unaided were required to do the whole work of haul- 
ing up the wire and sinker. 
he wire, though exposed to the sea-water, is preserved against rust by being 
kept constantly, when out of use, either immersed in or moistened with caustic 
nae The fact that steel and iron may be preserved from rust by alkali is well 
known to chemists, and is considered to result from the effect of the alkali in 
neutralizing the carbonic acid contained in the water, as the carbonic acid appears 
to be the chief cause of the rusting of steel and iron. 
This new method of sounding, depending on the use.of pianoforte wire, was first 
publicly explained by Sir Wm. Thomson im the Mechanical Section of the British 
Association at the Brighton Meeting two years ago; and in the interval which 
has since elapsed it has come rapidly into important practical use. 
I have to-day already brought under your notice a system of elaborately contrived 
and extensively practised methods of signalling and otherwise arranging for the 
safety of trains in motion on railways. These methods, in the aggregate, as we 
have them at present, may be looked on as the result of a gradual development, 
which, through design and intelligent selection, has been taking place during the 
last twenty or thirty years or more. In contrast with this I have now to mention 
a reform towards abatement of dangers at sea, which at present is only in an 
incipient stage of its practical application, but which, I am sure, must soon grow 
into one of the important reforms of the future. I refer to the provision of means 
whereby every important lighthouse shall, as soon as it is descried, not only make 
known to the navigator that a light is visible, but also that it shall give him the 
much more important information of what light it is,—that, in fact, it shall distin- 
guish itself to fien from all other lights either stationed on land or carried by ships 
out at sea. The rendering of lighthouses each readily distinguishable from every 
other light by rapid timed occultations was urged on public attention by Charles 
Babbage about twenty or twenty-three ago, in connexion with a like proposal of 
his for telegraphic signalling by occulting lights. His admirable idea, however, so 
far as it related to the distinguishing of lighthouses, has unhappily been left almost 
entirely neglected until quite recently. Although I say it was almost entirely 
neglected, yet very important steps in the direction of the object proposed were 
taken many years ago by Messrs. Stevenson, Engineers to the Commissioners of 
Northern Lights; and the flashing and intermittent lights introduced by them, and 
now used, although too sparingly, in various parts of the world, constituted a very 
great improvement in respect to distinctiveness. The first practical introduction of 
an intermittent extinction of a gas-light, which is a method now likely to hecome 
fruitful in important applications with further developments, was made many years 
ago by Mr. Wilson at Troon ; and an admirable application of this plan by the Messrs. 
Stevenson to carry out the principle of rapid signalling is to be seen in the Ardrossan 
Harbour light, which is alternately visible for two seconds, and then for two seconds 
is so nearly extinguished as to be invisible. The whole period—four seconds—is, 
I suppose, the shortest of any lighthouse in the world. This light fulfils the con- 
dition of being known to be the light which it is within five or ten seconds of its 
being first perceived ; and thus, in respect to distinctiveness, I trust that I may, 
without mistake, say it is the best light in the world. Mr. John Wigham has suc- 
ceeded in constructing large burners for the combustion of gas in lighthouses in 
general, including those of the first order, and embracing both i aa and 
1874 
