through the
eight lenses into eight pencils, having a divergence of about eight
degrees each, illuminated when at rest not quite fifty degrees of the
horizon; but when this system of lenses was put into rapid motion,
every degree of the three hundred and sixty degrees of the horizon
became illuminated, so that to spectators placed all round the horizon
the light would appear continuous and equally brilliant in every
direction. The only question would be, whether or not this continuous
light is essentially less intense than the light seen through the
lenses at intervals when in slow motion; and this is a point which
further inquiry must decide.

One of the causes which has tended to improve the brilliancy of
lighthouses, has produced inconveniences, which long existed without
remedy. During the combustion of a pound of oil, the union of its
hydrogen with the oxygen of the air produces more than a pound of
water in the state of vapour. When a cold wind is blowing upon the
lantern of the lighthouse from without, this vapour is condensed into
water upon the inner surface of the glass, and in very severe weather
forms a crust of ice, in some cases, as much as four inches thick in
the course of one night. This not only very much dims the brilliancy
of the light to the sailor, but also entails a great amount of labour
on the light-keepers, and injury to the lantern. The combustion of the
oil also produces a large quantity of carbonic acid gas, which is of a
very deleterious nature, and in many cases rendered the light-keepers'
rooms almost uninhabitable. Under these circumstances, the Trinity
House made application to Dr. Faraday to investigate the subject, with
a view to the discovery of some remedy. With his usual skill and
sagacity, Dr. Faraday instituted a number of inquiries and
experiments, and visited some of the principal lighthouses. The result
was the contrivance of a complete method of ventilating lighthouses.
On the dioptric system, the remedy was simple: it was merely to erect
a tall chimney over the central lamp, and lead it out at the roof; by
which means, the draught of the lamp was improved, and all the
products of combustion carried off. On the catoptric system, with
revolving lights, each lamp was furnished with a chimney, which passed
out at its upper extremity, through a small hole in the reflector into
a fixed central hollow shaft, which served the purpose of a
ventilating chimney to all the lamps. Thes