322 Royal Institution, 
has been yet established than the four-wicked Fresnel lamp in the 
centre of its dioptric and catadioptric apparatus. Now the electric 
light can be raised up easily to an equality with the oil lamp, and 
if then substituted for the latter, will give all the effect of the 
latter ; or by expenditure of money it can be raised to a five or 
tenfold power, or more, and will then give five- or tenfold effect. 
This can be done, not merely without increase of the volume of 
the light, but whilst the light shall have a volume scarcely the 2000th 
part of that of the oil flame. Hence the extraordinary assistance we 
may expect to obtain by diminishing the size, and perfecting the 
optical part of the apparatus. 
Many compressed intense lights have been submitted to the 
Trinity House; and that corporation has shown its great desire to 
advance all such objects and improve the lighting of the coast, by 
spending, upon various occasions, much money and much time for 
this end. It is manifest that the use of a lighthouse must be never 
failing, its service ever sure; and that the latter cannot be interfered 
with by the introduction of any plan, or proposition, or apparatus, 
which has not been developed to the fullest possible extent, as to the 
amount of light produced,—the expense of such light,—the wear 
and tear of the apparatus employed,—the steadiness of the light for 
16 hours,—its liability to extinction,—the amount of necessary 
night care,—the number of attendants,—the nature of probable 
accidents,—its fitness for secluded places, and other contingent 
circumstances, which can as well be ascertained out of a lighthouse 
asin it. The electric spark which has been placed in the South 
Foreland High Light, by Prof. Holmes, to do duty for the six win- 
ter months, had to go through all this preparatory education before 
it could be allowed this practical trial. It is not obtained from 
frictional electricity, or from voltaic electricity, but from magnetic 
‘action. The first spark (and even magnetic electricity as a whole) was 
obtained twenty-eight yearsago. (Faraday,PhilosophicalTransactions, 
1832, p.32.) If aniron core be surrounded by wire, and then moved 
in the right direction near the poles of a magnet, a current of elec- 
tricity passes, or tends to pass, through it. Many powerful magnets 
are therefore arranged on a wheel, that they may be associated very 
near to another wheel, on which are fixed many helices with their 
cores like that described. Again, a third wheel consists of magnets 
arranged like the first; next to this is another wheel of the helices, 
and next to this again a fifth wheel, carrying magnets. All the 
magnet-wheels are fixed to one axle, and all the helix wheels are 
held immoveable in their place. The wires of the helices are con- 
joined and connected with a commutator, which, as the magnet- 
wheels are moved round, gathers the various electric currents pro- 
duced in the helices, and sends them up through two insulated wires 
in one common stream of electricity into the lighthouse lantern. 
So it will be seen that nothing more is required to produce the 
electricity than to revolve the magnet-wheels, There are two 
magneto- electric machines at the South Foreland, each being put in 
motion by a two-horse power steam-engine ; and, excepting wear 
and tear, the whole consumption of material to produce the light is 
