THE ELECTRIC LIGHT. 
31 
between them, until at last the light is produced by carbons 
apparently in contact, and a small deposit of graphite is seen on 
the negative electrode. This deposit is about one-fourth the 
section of the positive carbon itself, and about one-eighth of an 
inch high. 
Mr. Werdermann places the negative carbon, in the form of a 
disc, two inches in diameter and an inch thick, uppermost. It 
is clasped by a copper band attached to one terminal. The 
lower positive electrode is a small pencil of carbon, three milli- 
metres in diameter, of any suitable length. It slides up ver- 
tically in a tube underneath the disc, projecting from it about 
three-quarters of an inch, this length being made incandescent 
when the current passes. It retains its point when burning. 
The carbons are kept in contact by chains passing over pulleys, 
and by a weight of about one and a half pounds pressing them 
gently into contact. 
One of the most important elements in the economical consi- 
deration of the electric light is the motive power. The great 
objection which lay at the root of all earlier systems intended 
to utilise electricity either as a motive power, as in Jacobi’s 
boat on the Neva, or as a source of light, was the expensive 
nature of the fuel required. The zinc consumed in the battery 
could only be produced at a cost which was practically pro- 
hibitory. The “ Electric Light, Power, and Colour Company,” 
started in 1855, endeavoured to evade this difficulty by using 
tin as the negative metal and utilising the refuse product for 
dyeing purposes. But this Company, though it brought out 
the excellent lamp of Mr. Chapman figured in the plate (PI. II.), 
which contains the germ of many more recent patents, was 
commercially a failure and soon collapsed. 
It was not until the invention of dynamo-electric machines 
had shown that motion, obtained without excessive waste, 
through the instrumentality of the steam-engine, from so cheap 
and abundant a fuel as coal, could be economically converted 
into electricity, that any financial comparison whatever between 
gas and the electric arc could be for a moment instituted. Even 
then there is an obvious disadvantage on the side of the latter, 
on account of the additional conversions of energy, with their 
attendant leakages in heat and friction, which it necessitates. 
Another difficulty, hardly if at all surmounted, now arises from 
the fact that electricity, as a source of light arising from intense 
and vehement action, is difficult to produce in moderate degrees, 
and hard to subdivide when once produced. It is not easy to 
realise in reading accounts of a light equal to 1 6,000 candles 
how far this is beyond the need of ordinary illumination. 
The first idea as to motors which occurs to the mind is the 
utilisation of great stores of energy which are daily running to 
