g its intensity by an
infinitesimal amount. The strengthened magnet instantly reacts upon
the coil which feeds it, producing a current of greater strength.
This current again passes round the magnet, which immediately brings
its enhanced power to bear upon the coil. By this play of mutual give
and take between magnet and armature, the strength of the former is
raised in a very brief interval from almost nothing to complete
magnetic saturation. Such a magnet and armature are able to produce
currents of extraordinary power, and if an electric lamp be introduced
into the common circuit of magnet and armature, we can readily obtain
a most powerful light. [Footnote: 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.] 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
electricity 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, endeavoured to turn this discovery to account for
lighthouse purposes. Already, in the spring of 1869, 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 splendour 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