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rent evidence, will any one be still bold enough to assert that the 
conservation of energy is a myth ? 
5.2. Examples without number might be adduced of the con- 
servation of energy, in which the equivalence has not yet been, but 
probably ere long will be, determined quantitatively; but a few 
must suffice. Whenever resistance is offered to the passage of 
an electric current, heat is generated in proportion to the 
resistance in the circuit, and the heat is evolved at the expense 
of current, that is to say, there is a transformation of electric 
into thermic energy; and this may exist in any degree, from the 
least perceptible elevation of temperature in the conductor, to 
its actual deflagration and volatilisation, as in the carbon points of 
an electric lamp, or the deflagration of gold-leaf by the discharge 
of a Leyden battery. And it has elsewhere been shown by the 
writer* that under suitable conditions the converse transforma- 
tion of heat into electricity takes place. If the adjacent ends 
of a bar of antimony (a) and one of bismuth ( b ) be soldered 
together, it has long been known that when a sufficiently weak 
current of electricity is transmitted through this thermo-electric 
element passing from a to b, heat is produced at the point of 
junction, but if passing in the direction from b to a , cold is pro- 
duced ; but when the element is placed in a Wheatstone’s 
bridge, the galvanometer shows a loss of current when heat is 
gained, and a gain of current when heat is lost. This leads 
irresistibly to the conclusion that an interchange of thermic and 
electric energy takes place at the point of junction of the two 
metals. It may be observed that bismuth presents this property 
in a higher degree than any other known substance ; and it is 
altogether a remarkable metal, excelling also in the property of 
diamagnetism, and sharing with water the property of expanding 
on passing from the fluid to the solid state by cooling. 
53. The dynamo-electric machine is another conspicuous 
example. While at rest it manifests no properties either of 
electricity or magnetism, but when kinetic energy produced by the 
muscular force of the arm is expended in turning the winch of the 
machine, magnetism is produced, and the electro-magnet becomes 
active; this again induces an electric current in the revolving 
armature, which in its turn becomes light and heat in a platinum 
wire, through which it may be transmitted ; or if employed in 
doing any mechanical work, it. becomes kinetic energy. 
54. Lastly, the sense of vision may be quoted as a highly 
probable example of the conservation of energy, it being not 
inconsistent with any known fact to suppose that the action of 
light on the retina is a true photographic process, not per- 
* L. E. and D. Phil. Mag., vol. xxxii., p. 378. 
