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ii8 DESIGN IN NATURE<br />
and heat, and indeed the phenomena of life, are due to the electrical energy which comes to us across the vacuum<br />
which exists between us and the sun—a vacuum which is pervaded by the ether, and which is a fit medium for<br />
the transition of the electro-magnetic waves."<br />
Clerk Maxwell propounded a great generalisation known as " the electro-magnetic theory of hght." Accord-<br />
ing to him all the phenomena of electricity, heat, and light are manifestations of electrical energy. Electricity under<br />
certain conditions produces heat and hght, and motion in turn produces all three. Electricity, heat, and light<br />
can be produced by friction or the rubbing of certain substances together. The trituration of even two pieces of ice,<br />
as Tyndall showed, generates enough heat to partly melt the ice. Coimt Rumford boiled water by rotatory and<br />
other movements as apart from fire, and Faraday demonstrated that a soft iron bar could be magnetised if placed<br />
within a coil of insulated copper wire through which an electric current was flowing. In such a case, the degree<br />
of magnetisation is increased by lengthening the coil of wire.<br />
These various transformations afford examples of the conservation of energy ; the direction of the energy<br />
being altered, while the energy itself is not dissipated or destroyed. One of the best examples of this great law is<br />
the formation of coal and the burning of it in the production of steam ; steam being, until lately, the chief generator<br />
of electricity as employed in the arts for propelling machinery, tram-cars, &c., and for producing artificial Ughting.<br />
The sun's rays (electro-magnetic in character) were required to grow the great tree ferns and other rank vegetation<br />
in the carboniferous era. The great tree ferns and their congeners lived, died, and were buried for long ages<br />
in the bowels of the earth. They were gradually transformed into coal, but the sun's heat and light, which<br />
originally assisted in the formation of the coal, though temporarily eclipsed, were not destroyed. The coal, when<br />
exhumed and burned, restores the heat and the light originally obtained from the sun, and can be employed in<br />
raising steam. Steam can be converted into motion, and motion into electricity, heat, and light. There is a<br />
cycle of apparently different results produced by one and the same cause. Electricity, heat, and light, as a matter<br />
of fact, are varieties of motion.<br />
Professor Faraday endeavoured to identify gravitation with electricity, heat, and light, but did not succeed,<br />
and at present we are wholly ignorant of the relations (if any) subsisting between gravitation and the<br />
others.<br />
There are those who endeavour to explain gravitation by movements occurring in the ether. They regard the<br />
ether as a vast ocean, with a definite tide, moving throughout space ; the ether passing through the sun and the<br />
planets with more or less difficulty ; its motion forcing the particles of matter together. The ether, as already<br />
stated, is beheved, and not unnaturally, to be the means by which the waves of electricity, heat, and hght are<br />
conveyed to us by the sun.<br />
"While Faraday failed to explain the nature of gravitation, he conferred untold advantages on what he regarded<br />
as cognate subjects by discovering induction and the conversion of motion into electricity. Whereas magnetism<br />
originally led the way to a knowledge of electricity, electricity, in turn, has thrown much light on magnetism.<br />
Weber and others have sought to explain the nature of magnetism by the so-called molecular theorJ^ They<br />
suppose that the molecules of a bar of iron form small magnets which, when the bar is unmagnetised, point indis-<br />
criminately in all directions, but when magnetised certain of them point in a definite direction. The theory holds<br />
good up to a point, but does not quite explain the action of magnetism on light, which compels us to assume a<br />
medium between the molecules, and to attribute rotatory or vortex movements to it. " There are not only<br />
attractive forces between the molecules of the iron, but also rotatory motion in the medium within and around<br />
the magnet."<br />
Since the discoveries of Professor Oersted in 1820, the chief interest has centred in the magnetic field or medium<br />
in which the attracting bodies are placed. Prior to this, no notice was taken of the surrounding medium, " and<br />
one magnetic pole was considered to act upon another as if it were an action at a distance and not from point<br />
to point in the medium between the attracting poles." Investigators did not recognise the Unes of force in the<br />
magnetic field, or the disturbance occasioned by them to a magnetic pole introduced into the field. They did not<br />
realise that the space around the earth is filled with lines of force which emerge and radiate from the north pole<br />
and curve round, converge, and re-enter the south pole. The magnetic field or medium, and the hnes of force<br />
pervading it, are now subjects for close scrutiny. " Faraday's great achievement was in his conception of the<br />
hnes of force which emanate from a magnetic pole and stretch through the ether of space ; in his pointing out<br />
that the medium surrounding the wires carrying electric currents, and the medium in wliich magnets are situated,<br />
is in a state of strain ; that there is what he called an electro-tonic state of this medium. It was like a mass<br />
of quivering jelly—any movement at one point producing a quiver in all neighbouring points."<br />
Maxwell, in his great work on electricity, thus speaks of Faraday's conception : " Faraday saw lines of force<br />
traversing all space where the mathematicians saw centres of force attracting at a distance. Faraday sought the