RECENT EXPERIMENTS ON FOG SIGNALS. 195 
of the Paris Alliance Company, of Wilde, and of Gramme, 
constitute a brilliant fulfillment of this prediction. 
But, as regards the augmentation of power, the greatest 
step hitherto made was independently taken a few years 
ago by Dr. Werner Siemens and Sir Charles Wheatstone. 
Through the application of their discovery a machine 
endowed with an infinitesimal charge of magnetism may, 
by a process of accumulation at compound interest, be 
caused so to enrich itself magnetically as to cast by its 
performance all the older machines into the shade. The 
light now before you is that of a small machine placed 
downstairs, and worked there by a minute steam-engine. 
It is a light of about 1,000 candles; and for it, and for the 
steam-engine that works it, our members are indebted to 
the liberality of Dr. William Siemens, who in the most 
generous manner has presented the machine to this Insti- 
tution. After an exhaustive trial at the South Foreland, 
machines on the principle of Siemens, but of far greater 
power than this one, have been recently chosen by the 
Elder Brethren of the Trinity House for the two light- 
houses at the Lizard Point. 
Our most intense lights, including the six-wick lamp, 
the Wigham gas-light, and the electric light, being in- 
tended to aid the mariner in heavy weather, may be 
regarded, in a certain sense, as fog-signals. But fog, when 
thick, is intractable to light. The sun cannot penetrate 
it, much less any terrestrial source of illumination. Hence 
the necessity of employing sound-signals in dense fogs. 
Bells, gongs, horns, whistles, guns, and syrens have been 
used for this purpose; but it is mainly, if not wholly, with 
explosive signals that we have now to deal. The gun has 
been employed with useful effect at the North Stack, near 
Holy head, on the Kish Bank near Dublin, at Lundy 
Island, and at other points on our coasts. During the 
long, laborious, and I venture to think memorable series of 
observations conducted under the auspices of the Elder 
Brethren of the Trinity House at the South Foreland in 
]872 and 1873, it was proved that ashortS-^-inch howitzer, 
firing 3 Ibs. of powder, yielded a louder report than a long 
18-pouuder firing the same charge. Here was a hint to be 
acted on by the Elder Brethren. The effectiveness of the 
sound depended on the shape of the gun, and as it could 
not be assumed that in the howitzer we had hit accident- 
