NATURAL PHILOSOPHY. Ill 



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 as in it. The electric spark which has been placed in the South 

 Foreland High Light, by Professor Holmes, to do duty for the six winter 

 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 years ago. 

 (Faraday, Philosophical Transactions, 1832, p. 32.) If an iron core be sur- 

 rounded by wire, and then moved in the right direction near the poles of a 

 magnet, a current of electricity passes, or tends to pass, through it. Many 

 powerful magnets are therefore arranged on a wheel, that they may be asso- 

 ciated very near to another wheel, on which are fixed many helices with their 

 cores like that described. Again : A third wheel consists of magnets ar- 

 ranged 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 immovable in their place. The 

 wires of the helices are conjoined and connected with a commutator, which, 

 as the magnet wheels are moved round, gathers the various electric currents 

 produced 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 Avheels. 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 the coke and water required to raise steam for the engines and car- 

 bon points for the lamp in the lantern. The lamp is a delicate arrangement 

 of machinery, holding the two carbons between which the electric light 

 exists, and regulating their adjustment; so that whilst they gradually con- 

 sume away, the place of the light shall not be altered. The electric wires 

 end in the two bars of a small railway, and upon these the lamp stands. 

 When the carbons of a lamp are nearly gone, that lamp is lifted off and 

 another instantly pushed into its place. The machines and lamp have done 

 their duty during the past six months in a real and practical manner. The 

 light has never gone out through any deficiency or cause in the engine and 

 machine house, and when it has become extinguished in the lantern, a single 

 touch of the keeper's hand has set it shining as bright as ever. The light 

 shone up and down the Channel, and across into France, with a power far 

 surpassing that of any other fixed light within sight or anywhere existent. 



To show the necessity for an intense light in lighthouse illumination, Dr, 

 Faraday reminded his audience of the dark shadow thrown by the steam is- 

 suing from a railway locomotive on a sunshiny day; and, having cast a con- 

 centrated light from the electric lamp upon a screen, he showed how instan- 

 taneously it was darkened by an artificial cloud made of high pressure steam, 

 and which might be taken as an illustration of the effect of the sea fogs and 

 mists so common near the coast. 







ELECTRIC LIGHT TELEGRAPH. 



Mr. Caselli purposes to employ the electric light for telegraphic purposes 

 during war, or in situations that do not admit of the usual communication 

 by wire. Signals like those of Morse would be represented by two lengths 



