25 
THE ELECTEIC LIGHT. 
By W. H. STONE, M.D. 
[Plate II.] 
Theee has been no lack of material for the increased public 
interest ■which has of late been exhibited in the practical de- 
velopment of science ; and the last instance differs materially 
from its forerunners in the great technical and everyday im- 
portance which it possesses. Even Telephones and Phonographs 
are far exceeded in popular attention by inventions which pro- 
pose to revolutionize the system of general illumination, and to 
supersede coal-gas — a means of lighting which, though introduced 
within the memory of many still living, has become so familiar 
as to be unnoticed. There can be little doubt, moreover, that 
this popular excitement, though it may not have been intention- 
ally stimulated by sensational announcements, has derived a 
peculiar zest and pungency from the financial results it has 
brought about. The great depreciation in shares of gas com- 
panies which followed Mr. Edison’s announced, but still unex- 
plained, discovery, not only set in motion the world of speculators 
and financiers, but led the consumer at large to hope for partial 
or complete emancipation from one of his old tyrants, and for 
the substitution of an immensely superior method of lighting. 
And yet the Electric Light is, strictly speaking, no new 
subject. Produced by Sir Humphry Davy, at the beginning of 
the century, from his large battery of 3,000 cells, it has been 
ever since an essential of the laboratory, and has for many years 
been occasionally exhibited in public. 
A great impetus was, however, given to its study by Fara- 
day’s discovery, in 1831, of the induction of currents by magnets, 
thus dispensing with the expensive and troublesome battery. 
Machines of this nature were constructed in 1849 by Holmes, 
and by the Alliance Company of Paris, which have worked satis- 
factorily at the South Foreland, Cape Grisnez, and several other 
lighthouses, for many years. 
The current is here produced from armatures rotating in 
front of fixed permanent magnets, arranged symmetrically round 
