as to refract these
beams into parallel rays in the required directions.

Lenses were employed in lighthouses at a very early period. When they
were first made they were used for burning instruments, by collecting
the rays of the sun. It was seen, however, that they would equally
collect the rays of a lamp. They have of late years been very greatly
improved by a celebrated glass manufacturer. Great indeed has been the
improvement in lighthouses. Once upon a time they were simply high
towers, which had on their summits open fireplaces, in which either wood
or coal fires were burned. They were often unserviceable at the very
time their services were most required. During a heavy gale, for
instance, when the wind was blowing towards the land, it drove the
flames of an open fire away from the direction in which they were most
wanted to be seen. Sometimes, in fog or rain, the glare of the fire was
visible by refraction in the atmosphere, although the fire itself could
not be seen. Such was the tower of the North Foreland. This lighthouse
existed in 1636, and merely had a large glass lantern fixed on the top
of a timber erection, which, however, was burnt in 1683. Towards the
end of the same century a portion of the present structure was raised,
having an iron grate on the summit. It being found difficult to keep a
proper flame in windy or rainy weather, about 1782 it was covered in
with a roof and large sash windows, and a coal fire was kept alight by
means of enormous bellows, which the attendants worked throughout the
night.

This very primitive means of maintaining a light was exchanged in 1790
for a lantern, with lamps and other apparatus. The Eddystone lighthouse
was from the first illuminated by means of a chandelier, containing
twenty-four wax candles, five of which weighed two pounds. The
Liverpool lighthouses had oil lamps, with rude reflectors. Down to the
year 1823 coal fires were used in several lighthouses. Really good
lights have come into universal use only during the last few years; and
it is said that on the west coast of Sweden a coal fire is still used at
an important lighthouse.

The Argand lamp is generally employed in lighthouses. It was the
greatest advance in artificial lighting until the introduction of gas.
It was discovered by Monsieur Argand, a citizen of Geneva. He was
trying experiments with a common lamp he had invented. A younger
brother describes its accidental discover