504 
NATURE 
the lighthouses and light-vessels of the world ; and, as their 
numbers increase, so does the necessity for giving a more clearly 
dlistinctive character to each light over certain definite ranges 
of coast. This important question of affording to each lisht 
complete distinctive individuality is receiving the attention of 
lighthouse authorities at home and abroad, and it is hoped that 
greater uniformity and consequent benefit to the mariner will 
be the result. 
During the old days of sailing-vessels, when the duration of 
voyages was so uncertain, sound-signals, as aids to the mariner, 
were but little demanded. The seaman on approaching the 
coast in fog trusted entirely to his lead, and, when he found 
circumstances favourable for doing so, he anchored his vessel 
until the atmosphere cleared. But, since the application of 
steam to navigation, with keener competition in trade, these 
conditions have been entirely changed. The modern steam- 
vessel is expected to keep time with nearly the same degree of 
precision as a railway train, and it is evident that, even with the 
utmost care and attention onthe part of her commander, this 
requirement cannot possibly be fulfilled, and collisions and 
strandings must occur, unless efficient sound-signals for fog be 
carried by each vessel, and powerful signals of this class be pro- 
vided at lighthouse and light- vessel stations. 
These circumstances have led to a rapid development of fog- 
signals, both ashore and afloat, there being now about 700 of 
these signals, of various descriptions, on the coasts of the world. 
We therefore find, as might have been naturally expected, that 
coast fog-signals have been made, by lighthouse authorities, the 
subject of careful experiment and scientific research ; but, un- 
fortunately, the practical results thus far have not been so satis- 
factory as could bz desired, owing (1) to the very short range of 
the most powerful of these signals under occasional unfavourable | 
conditions of the atmosphere during fog ; and (2) to the present 
want of a reliable test for enabling the mariner to determine at 
any time how far the atmospheric conditions are against hin in 
listening for the anxiously expected signal. In 1854 some 
experiments on different means of producing sounds for coast 
fog-signals were made by the engineers of the French light- 
house department, and in 1861-62 MM. Le Gros and Suint- 
Ange Allard, of the Corps des Ponts et Chausées, conducted a 
series of experiments upon the sound of bells and the various | 
methods of striking them, 
In 1863-64 a Committee of the Elder Brethren of the Trinity 
House made some experiments at Dungeness upon various fog- 
signals, In June 1863 a Committee of the British Association 
memorialised the then President of the Board of Trade, with 
the view of inducing him to institute a series of experiments 
upon fog-signals. The memorial, after briefly setting forth a 
statement of the nature and importance of the subject, described 
what was then known respecting it, and several suggestions 
were made as to the nature of the experiments recommended. 
The proposal does not appear to have been favourably enter- 
tained by the authoritie, to whom it was referred, and the 
experiments were not carried out, 
In 1864 a series of experiments was undertaken by a Com- 
mission appointed by the Lighthouse Board of the United 
States, to determine the relative powers of various fog-signals 
which were brought to the notice of the Board. 
In 1872 a Committee of the Trinity House visited the United 
States and Canada, with the object of ascertaining the actual 
efficiency of various fog-signals then in operation on the North 
American continent, about which very favourable reports had 
reached this country. Among other instruments, they witnessed 
the performance of a Siren apparatus, patented by Messrs. A. 
and F. Brown, of New York. One of these instruments was, 
in 1873, very kindly sent to the Trinity House by the United 
States authorities, and tested with other instruments in the ex- 
perimental trials at the South Foreland in 1873-74. This in- 
vestigation was carried out at the South Foreland by the Trinity 
House, with the object of obtaining some defitite knowledge as 
to the relative merits of different sound-producing instruments, 
and also of ascertaining how the propagation of sound was 
affected by meteorological phenomena. These experiments 
were extended over a lengthened period, in all conditions of 
weather ; and the well-known scientific and practical results 
obtained, together with the ascertained relative merits of sound- 
producing instruments for the service of the mariner, are of the 
highest scientific interest and practical importance. 
The investigation at the South Foreland was followed up by 
the Trinity House by further experiments, in which they were 
| the fittest of all those at present known to science. 
assisted by the authorities at Woolwich, with guns of various 
forms, weight of charges, and deseripiions of gunpowder. The 
powders tested were (1) fine grain, (2) larger grain, (3) rifle 
large grain, and (4) pebble. The result placed the powders 
exactly in the order above stated; the fine grain, or most 
rapidly burning powder, gave indisputably the loudest sound, 
while the report of the slowly-burning pebble powder was 
the weakest of them all. Experiments were als> made with the 
object of ascertaining the relative value of the sound produced 
by the explosion of varying quantities of gun-cotton. 
again the greater value of increased rapidity of com ustion in 
producing sound was clearly demonstrated. It was found that 
charges of gun-cotton yielded reports louder at all ranges than 
equal charges of gunpowder, and further experiments proved 
that the explosion of half a pound of gun-cotton gave a result 
at least equal to that produced by 3 lb. of the best gunpowder. 
These results led the Trinity House to adopt this explosive as a 
fog-signal for isolated stations on rocks or shoals where pre- 
viously, from want of space, nothing better than a bell could 
be applied, It is also applied with success to light-vessels. 
But, wherever the Siren can be installed, it is found to be the 
most efficient fog-signal yet known, chiefly in consequence of 
the prolongation that can be given to its blasts, and the ease 
with which it can be applied, with any amount of motive-power 
available, to the production of any desired combination of high 
and low notes for distinctions corresponding with those of white 
and red, or short and long, flashes of light, and thus affording 
the required individuality of each station. The experience, 
however, with the most powerful fog-signal is not at present to 
be considered altogether satisfactory. With Siren blasts absorb- 
ing about 150 H.P., or nearly 5,000,000 foot-pounds, per minute 
during the time they are sounding, the signal is occasionally not 
heard, under some conditions of fog and wind, beyond 1 mile, 
while at other times it is distinctly heard above 10 miles. 
In 1881 it was considered by the lighthouse authorities of this 
country that the time had arrived when it was absolutely neces- 
sary that an exhaustive series of experimental trials should be 
made, on a practical scale, for the exact determination of the 
relative merits (both as regards efficiency and economy) of the 
three lighthouse illuminants, electricity, gas, and mineral oil, 
which, by the process of natural selection, may be regarded as 
After many 
unforeseen difficulties had been overcome, this question of 
universal importance was, in July 1883, referred by the Board 
of Trade to the Trinity House, who accepted the responsibility 
of carrying out the investigation. 
A Committee was formed of members of the Corporation, 
who secured the friendly co-operation of the Scotch and Irish 
Lighthouse Boards, and many distinguished scientific men at 
home and abroad. I had the honour of acting, in my official 
capacity as Engineer-in-Chief to the Trinity House, in making 
the arrangements for exhibiting the experimental lights, and in 
reporting to the Board from time to time, as in all other matters 
referred to me professionally. 
These investigations were carried out in full view of all who 
were in any way interested in the subject. The whole arranze- 
ments were open to public inspection, and, in their desire to 
arrive at a wise and just decision on so important a question, the 
Trinity House Committee courted the fullest inquiry. Many 
members of scientific Societies, especially those connected with 
engineering, were invited, and visited the station. The French 
lighthouse authorities, who rendered much kind assistance in 
obtaining observations, sent their representatives to view the 
arrangements, and officers from the lighthouse services of Ger- 
many, Denmark, Norway aid Sweden, Russia, Italy, Spain, 
Brazil, the United States, and Canada visited the station and 
witnessed the experiments. 
In order to obtain, with uniformity and method, a consensus 
of comparative eye-measurements—in addition to the measure- 
ments of the Comittee and their officers at their different stations 
ashore and afloat, to those of the coastguard men at nine stations 
between Dungeness and the North Foreland, and to the more 
precise scientific measurements of the experts—special observa- 
tion-books were prepared, and widely distributed to shipping 
associations and port authorities, with a view to their securing 
the co-operation of masters of vessels, pilots, and others navigat- 
ing in the vicinity of the South Foreland. 
The South Foreland Station is especially adapted for light- 
house experiments generally, because of the existing facilities 
for observations on land and sea. The land in the neizhbour- 
[ Sept. 23, 1886 
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