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MAGNETISM, ELECTRICITY, LIGHT, HEAT, AND MOTION 117<br />
we call light. According to this theory, the displacements of the ether will produce a disturbance of the vortices,<br />
and this disturbance of the vortices can be supposed to react on the ether, and in this way can affect the pro-<br />
pagation of Ught." ^<br />
If a Leyden jar be discharged through a great circle of wire placed in one room, electro-magnetic waves can be<br />
sent through brick walls and detected in another room by the sparks excited in a similar circle of wire connected<br />
with a second Leyden jar. The electro-magnetic waves undulate in the direction of their length ; they also<br />
undulate athwart the path of the wave's advance. " The ether, though homogeneous and continuous, may be, as<br />
regards its density, rendered heterogeneous by motion (' Hypotheses of Vortex Molecules,' by Lord Kelvin). Magnetic<br />
influence on light indicates a rotational motion of the media when magnetised. This motion does not imply a<br />
dissipation of energy." No substance cuts of! the lines of magnetic force : they pass through wood, stone walls,<br />
copper, and all metals. Ether transmits transverse vibrations to very great distances without sensible loss of<br />
energy. Ordinary atmospheric air can transmit waves of sound which move to and fro in the direction in which<br />
they are propagated. It cannot, however, transmit waves of heat, Ught, and electricity, which require transverse<br />
vibrations and the presence of ether. A good illustration of heat and Ught waves is obtained by throwing a<br />
stone into a placid pool of water. The waves spread in ever-widening circles fi'om the centre of disturbance, and<br />
indicate the direction of progress. They have also a vertical movement at right angles (transverse in character)<br />
in addition to the spreading movement.<br />
As there is no limit to space, and ether (or its equivalent) occupies all space, electrical and other movements<br />
are propagated to all parts of the universe, and hence the possibihty<br />
of wireless telegraphy, which is mainly due to molecular vibrations and<br />
pulsations of the ether in space. The same is true of the telephone,<br />
where the 'nbrations are originally produced by the vocal chords<br />
(human voice) or other sounding bodies. The vibrations are, in the<br />
first instance, conveyed to a thin vibrating disc, which, having to-and-<br />
fro movements communicated to it, causes the molecules in space to<br />
react upon each other in waves to a practically unUmited extent. The<br />
vibrations generated in one locahty can be collected by a duplicate<br />
vibrating disc in another, with the result that messages can be trans-<br />
Fig. 23.—Diagi-am of telephone (after Trowbiidge).<br />
mitted incredibly long distances.^ This extraordinary achievement is only possible when there is unhmited matter<br />
and motion : any breach of continuity either in the matter or the motion would be fatal to the principle and<br />
practice of wireless telegraphy and telephony. The telephone, a sketch plan of which is appended (Fig. 23), is<br />
an instrument based entirely on Faraday's discovery of magnetic induction. It was discovered by Professor<br />
Graham Bell, who has acquired a great reputation as an authority in the physics of sound.<br />
The electric telegraph (discovered before the telephone by Morse and others) acts on essentially the same<br />
principle as the telephone. Both transmit messages by means of electro-magnets and insulated wires ; the earth<br />
in certain cases acting as a return wire. Dynamo machines, electro-magnets, and insulated wires perform the<br />
bulk of electric work. Electricity, Hke heat and Ught, as already indicated, is regarded as a form of motion ;<br />
the only difference between electricity, heat, and Ught consisting in the length of the waves. The waves of heat,<br />
for example, approximate to those of electricity, and are longer than those of Ught. " AU space is fiUed with<br />
a medium which transmits electro-magnetic waves to us from the sun." The sun, which is the source of the<br />
electro-magnetic waves, has been compared to an enormous electrical furnace, consisting of a mass of molten metals<br />
where carbon is freed from its impurities, and the metals driven off in vapour. The presence of oxygen in the sun<br />
seems necessary to account for the exceeding splendour and brilliancy of that magnificent orb. Faraday and Dewar<br />
have shown that oxygen is strongly magnetic.^<br />
" We have already strong grounds for believing that we hve in a medium which conveys to-and-fro or periodic<br />
movements to us from the sun, that these movements are electro-magnetic, and that all the transformations of Ught<br />
' Trowbridge, op. cit. pp. 264, 265, 272 and 273.<br />
^ As to the distance which may be covered by wireless telegraphy the annexed report by Signer Marconi's assistant in the Scvlsiiian of<br />
March 12, 1907 is at once instructive and impressive :— "Nine years have passed since the writer became assistant to M. Marconi at the first<br />
raodei-n wireless telegraph station. The distance over which messages were transmitted was not great, only about 14 miles, but the transmission<br />
was regular, if slow, and suffered but little from interruptions. Previous wireless systems, such as those of Morse, Lindsay, Willoughby-Sniith,<br />
Stevenson, and Preece, had been based on different principles, and had never attained to distances above a very few miles. Great distance is now<br />
a matter of so little notice that few people are even aware that there are at least a dozen wireless stations in different parts of the world which<br />
maintain regular telegraphic communication with others which are over a thousand miles off. The Atlantic Ocean is 3000 miles wide, but<br />
the gi-eat Cunarders are never out of direct touch with either England or America. Panama is connected directly with Manhattan Beach, 2170<br />
miles distant, and recent results show that Boston, though 3000 miles off, will be veiy shortly in permanent conmmnication witli Machrihanish,<br />
in Kintyre."<br />
' Oxygen is said to constitute the largest portion of the solid and liquid substances of our planet so far as we know it and ; nitrogen is<br />
by far the predominant constituent of our atmosphere.