12 
“ On some Improved Methods of Producing and Regula- 
ting Electric Light,” by Henry Wilde, Esq. 
Among the manifold functions which the elementary 
substance carbon performs in organic nature, not the least 
important is that by which it becomes the great source of 
artificial illumination, whether derived from oils, coal gas, or 
from coke rendered incandescent by the action of powerful 
electric currents. Since the time when Davy first produced 
the voltaic arc, between two points of wood charcoal, through 
which was transmitted the current from the great battery 
of 2000 plates belonging to the Royal Institution, many ex- 
periments have been made to determine the best kinds of 
carbon for developing the electric light. The carbon which, 
until recently, was most commonly employed for this pur- 
pose, is obtained from the sides of gas retorts, where it ac- 
cumulates in the form of coke during the destructive dis- 
tillation of coal. The shells of coke from the retort are sawn 
up into pencils from one quarter, to half an inch square, 
and from six to nine inches in length. Although very good 
results are obtained from carbon of this kind, it is a difficult 
material to work on account of its hardness, and it some- 
times contains impurities which interfere with its conduct- 
ivity. It is also liable to fracture when suddenly heated by 
the transmission of powerful electric currents. These defects 
have led to the introduction in electric lighting of artificial 
carbon, composed of powdered coke and lamp black, formed 
into a paste with molasses and gum. This material is pressed 
into cylindrical forms, and subjected for a given time to a 
high temperature in a special furnace. The manufacture of 
these carbon pencils has attained great perfection in the 
hands of Carre of Paris, and they can be made into perfectly 
straight and cylindrical forms of from two to sixteen milli- 
metres in diameter, and half a metre in length 
When the electric light is to be used for illumination, it 
is necessary that it should be as continuous as other modes 
