ii8 DESIGN IN NATURE 



and heat, and indeed the phenomena of life, are due to the electrical energy which comes to us across the vacuum 

 which exists between us and the sun — a vacuum which is pervaded by the ether, and which is a fit medium for 

 the transition of the electro-magnetic waves." 



Clerk Maxwell propounded a great generalisation known as " the electro-magnetic theory of hght." Accord- 

 ing to him all the phenomena of electricity, heat, and light are manifestations of electrical energy. Electricity under 

 certain conditions produces heat and hght, and motion in turn produces all three. Electricity, heat, and light 

 can be produced by friction or the rubbing of certain substances together. The trituration of even two pieces of ice, 

 as Tyndall showed, generates enough heat to partly melt the ice. Coimt Rumford boiled water by rotatory and 

 other movements as apart from fire, and Faraday demonstrated that a soft iron bar could be magnetised if placed 

 within a coil of insulated copper wire through which an electric current was flowing. In such a case, the degree 

 of magnetisation is increased by lengthening the coil of wire. 



These various transformations afford examples of the conservation of energy ; the direction of the energy 

 being altered, while the energy itself is not dissipated or destroyed. One of the best examples of this great law is 

 the formation of coal and the burning of it in the production of steam ; steam being, until lately, the chief generator 

 of electricity as employed in the arts for propelling machinery, tram-cars, &c., and for producing artificial Ughting. 

 The sun's rays (electro-magnetic in character) were required to grow the great tree ferns and other rank vegetation 

 in the carboniferous era. The great tree ferns and their congeners lived, died, and were buried for long ages 

 in the bowels of the earth. They were gradually transformed into coal, but the sun's heat and light, which 

 originally assisted in the formation of the coal, though temporarily eclipsed, were not destroyed. The coal, when 

 exhumed and burned, restores the heat and the light originally obtained from the sun, and can be employed in 

 raising steam. Steam can be converted into motion, and motion into electricity, heat, and light. There is a 

 cycle of apparently different results produced by one and the same cause. Electricity, heat, and light, as a matter 

 of fact, are varieties of motion. 



Professor Faraday endeavoured to identify gravitation with electricity, heat, and light, but did not succeed, 

 and at present we are wholly ignorant of the relations (if any) subsisting between gravitation and the 

 others. 



There are those who endeavour to explain gravitation by movements occurring in the ether. They regard the 

 ether as a vast ocean, with a definite tide, moving throughout space ; the ether passing through the sun and the 

 planets with more or less difficulty ; its motion forcing the particles of matter together. The ether, as already 

 stated, is beheved, and not unnaturally, to be the means by which the waves of electricity, heat, and hght are 

 conveyed to us by the sun. 



"While Faraday failed to explain the nature of gravitation, he conferred untold advantages on what he regarded 

 as cognate subjects by discovering induction and the conversion of motion into electricity. Whereas magnetism 

 originally led the way to a knowledge of electricity, electricity, in turn, has thrown much light on magnetism. 

 Weber and others have sought to explain the nature of magnetism by the so-called molecular theorJ^ They 

 suppose that the molecules of a bar of iron form small magnets which, when the bar is unmagnetised, point indis- 

 criminately in all directions, but when magnetised certain of them point in a definite direction. The theory holds 

 good up to a point, but does not quite explain the action of magnetism on light, which compels us to assume a 

 medium between the molecules, and to attribute rotatory or vortex movements to it. " There are not only 

 attractive forces between the molecules of the iron, but also rotatory motion in the medium within and around 

 the magnet." 



Since the discoveries of Professor Oersted in 1820, the chief interest has centred in the magnetic field or medium 

 in which the attracting bodies are placed. Prior to this, no notice was taken of the surrounding medium, " and 

 one magnetic pole was considered to act upon another as if it were an action at a distance and not from point 

 to point in the medium between the attracting poles." Investigators did not recognise the Unes of force in the 

 magnetic field, or the disturbance occasioned by them to a magnetic pole introduced into the field. They did not 

 realise that the space around the earth is filled with lines of force which emerge and radiate from the north pole 

 and curve round, converge, and re-enter the south pole. The magnetic field or medium, and the hnes of force 

 pervading it, are now subjects for close scrutiny. " Faraday's great achievement was in his conception of the 

 hnes of force which emanate from a magnetic pole and stretch through the ether of space ; in his pointing out 

 that the medium surrounding the wires carrying electric currents, and the medium in wliich magnets are situated, 

 is in a state of strain ; that there is what he called an electro-tonic state of this medium. It was like a mass 

 of quivering jelly— any movement at one point producing a quiver in all neighbouring points." 



Maxwell, in his great work on electricity, thus speaks of Faraday's conception : " Faraday saw lines of force 

 traversing all space where the mathematicians saw centres of force attracting at a distance. Faraday sought the 



