t:—_ ENGINEERING. 179 
Cooke and Wheatstone used electromagnets, which Sturgeon had dis- 
covered in 1825, instead of permanent magnets. It was during the 
years 1865 to 1873 that the shunt and series self-excited dynamo, using a 
ring or drum armature and a commutator of many segments, finally 
evolved. 
The early workers in the field do not appear to have realised the 
intimate connection between the dynamo and the motor, for, although 
the principle was discovered by Lenz in 1838, it only appears to have 
become generally known that the same machine could be used for either 
purpose about 1850. The principle underlying the whole modern develop- 
ment of electrical engineering—viz., the generation of electrical power by a 
dynamo, its transmission to a distant point and its re-transformation to 
mechanical power by an electric motor—appears to have evolved about 
1873. An interesting light is thrown on the subject by a paper read before 
the Institution of Civil Engineers in 1857 by Mr. Hunt on ‘ Electromagnetism 
as a Motive Power.’ In this paper the possibility of driving electro- 
magnetic engines—that is, electric motors—by currents derived from 
voltaic batteries was discussed in the light of Jacobi’s discovery of the 
back-electromotive force in these machines. He concluded that power so 
generated would be sixty times as dear as steam-power, and that it would 
be far more economical to burn the zinc under a boiler than to consume 
it in a battery for generating electromagnetic power. The leading scientists 
and engineers who took part in the debate all agreed that electromotive 
power was unpractical and impossible commercially. William Thomson 
sent a contribution in writing which concluded with the following 
sentence: ‘Until somemode is found of producing electricity as many times 
cheaper than that of an ordinary galvanic battery as coal is cheaper than 
zinc, electromagnetic engines cannot supersede the steam engine.’ As 
S. P. Thompson says, ‘ Faraday’s great discovery of 1831 notwithstanding, 
the real significance of the dynamo had not yet (in 1857) dawned upon the 
keenest minds of the time.’ Six years before this, Thomson had suggested 
the experiment of driving a ‘ galvanic engine’ from a thermal battery, 
and had stated the problem in terms which show that he already had a 
correct grasp of the theory of the efficiency of the electric motor. 
It was at the Manchester Meeting of the British Association in 1861 
that Charles Bright and Latimer Clark read a paper proposing names for 
the principal electrical units; the names were ‘ galvat’ for current, 
‘ohma’ for electromotive force, ‘farad’ for quantity, and ‘ volt’ for 
resistance. This paper led to the appointment of the celebrated Electrical 
Standards Committee of the British Association, which, after six years 
of strenuous work, produced the system now adopted internationally. 
One of the earliest applications of the dynamo was for lighting arc 
lamps in lighthouses ; in 1863 Thomson, writing to a friend on the relative 
merits of the Holmes direct-current and the Nollet alternating-current 
lighthouse machines, says: ‘Thus Nollet escapesthe commutator, a great evil, 
and gets a flame which does not burn one of the points faster than the 
other. The reverse of each proposition applies to Holmes. The commutator 
is a frightful thing ... the thing to be done at the requisite speed is appal- 
ling. However, Holmes does it successfully. But I believe it cannot be 
done except theoretically without great waste of energy and consequent 
burning of contact surfaces... . But I believe a large voltaic battery will be 
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