keeper; and, accordingly, we were invited to intrust ourselves to his
guidance.

He informed us that the structure rested on a foundation consisting of a
concrete mass, nine feet below the water line. Having ascended four
flights of iron-wrought winding stairs, we reached the top of the circular
structure; it having a diameter of twenty-four feet at its base, and
rising to an elevation of fifty-seven feet.

With great interest we inspected the revolving lights, exhibiting an
ingenious piece of machinery, the invention of Finisterre and Barren in
Paris, and representing a value of $1,800. This apparatus for rotating
lamps is far superior to that for a fixed light.

The characteristic of the latter is to constantly illuminate the whole
horizon, requiring all the rays to fall simultaneously on the navigable
track, whereas the demands made of a revolving light, are not nearly so
great; only each point of the horizon being lighted at successive periods.

When the dark intervals occur, the rays from the flame which are then
pointing toward the obscure spaces, have their direction so altered
laterally as to pass into the adjoining bright places; and so increase the
power of the luminous flashes. A revolving light, though supplied by a
flame of the same strength as a fixed, will thus necessarily be raised to
a higher degree; for it does not lose its power by diffusing the rays
constantly over the whole horizon, but gathers them up into a number of
separate beams of greater intensity.

The lights made to revolve by means of clockwork, were fed with mineral
oil, a refined kerosine; and the refraction was caused by highly polished