products of combustion. An electric current from a battery is the only source possible. The fact that the Planté battery requires recharging from time to time gives rise to no difficulty because the submarine spends most of its life on the surface of the water and can then charge the batteries from its engines. But with regard to the work below the surface, the secondary battery is alone capable of satisfying the necessary requirements of the submarine so that the laboratory work of this quiet scientist made possible the Submarine Menace.
The next great scientific discovery which has proved a formative factor in this War is Wireless Telegraphy. It is rightly regarded as a recent gift of Science to mankind. Yet in its essence it does not differ from the heliographic signals that are still sent from the hills to the plains in India and elsewhere. In both cases waves of electro-magnetic disturbance are sent and received. But when light is the transmitting agency these waves are generated by the heat of the sun and perceived by the human eye.
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