18 
property of the alternating current to which I have directed 
attention. 
As I have already said, the strength of the alternating 
current must hear a proper proportion to the diameter of 
the carbons used, and when a number of such lights are 
required to be produced in the same circuit, the quantity 
and property of the current will remain constant, while the 
tension will require to be increased with the number of 
lights. 
This simple method of burning the carbons will, I believe, 
greatly further the development of the electric light, as the 
carbons can be used of much smaller diameter than has 
hitherto been possible. They may also be of any desired 
length, for as they are consumed they may be pushed 
up through the holders without interrupting the light. 
One of these developments will be a better method of 
lighting coal and other mines. In this application the 
alternating currents or waves from a powerful electro- 
magnetic induction machine may be used for generating, 
simultaneously, alternating secondary currents or waves in 
a number of small induction coils, placed in various parts of 
the mine. The light may be produced in the secondary 
circuits from pairs of small carbons enclosed in a glass 
vessel having a small aperture to permit the expansion of 
the heated air within. Diaphragms of wire gauze may be 
placed over the aperture to prevent the access of explosive 
gas. By generating secondary currents or waves without 
interrupting the continuity of the primary circuit, the con- 
tact breaker is dispensed with, and the subdivision of the 
light may be carried to a very great extent. 
