(J72 PR A GMENTS F SCIENCE. 
electric lamp be introduced into the common circuit of 
magnet and armature, we can readily obtain a most power- 
ful light.* By this discovery, then, we are enabled to 
avoid the trouble and expense involved in the employment 
of permanent magnets; we are also enabled to drop the 
exciting magneto-electric machine, and the duplication of 
the electro- magnets. By it, in short, the electric generator 
is so far simplified, and reduced in cost, as to enable elec- 
tricity to enter the lists as the rival of our present means of 
illumination. 
Soon after the announcement of their discovery by 
Siemens and Wheatstone, Mr. Holmes, at the instance of 
the Elder Brethren of the Trinity House, endeavored to 
turn this discovery to account for lighthouse purposes. 
Already, in the spring of 18G9, he had constructed a 
machine which, though hampered with defects, exhibited 
extraordinary power. The light was developed in the 
focus of a dioptric apparatus placed on the Trinity Wharf 
at Blackwall, and witnessed by the Elder Brethren, Mr. 
Douglass, and myself, from an observatory at Charlton, on 
the opposite side of the Thames. Falling upon the 
suspended haze, the light illuminated the atmosphere for 
miles all round. Anything so sunlike in splendor had not, 
I imagine, been previously witnessed. The apparatus of 
Holmes, however, was rapidly distanced by the safer and 
more powerful machines of Siemens and Gramme. 
As regards lighthouse illumination, the next step forward 
was taken by the Elder Brethren of the Trinity House in 
1876-77. Having previously decided on the establishment 
of the electric light at the Lizard in Cornwall, they 
instituted, at the time referred to, an elaborate series of 
comparative experiments wherein the machines of Holmes, 
of the Alliance Company, of Siemens, and of Gramme, 
were pitted against each other. The Siemens and the 
Gramme machines delivered direct currents, while those 
of Holmes and the Alliance Company delivered alternating 
currents. The light of the latter was of the same intensity 
in all azimuths; that of the former was different in 
different azimuths, the discharge being so regulated as to 
yield a gush of light of special intensity in one direction. 
* In 1867 Mr. Ladd introduced the modification of dividing the 
armature into two separate coils, one of which fed the electro-magnets, 
while the other yielded the induced currents. 
