bable
use upon the Scottish coast. A considerable time was occupied in
inquiry and negotiation, when at length, on the 26th October, 1836,
the light at the Isle of May was changed from the catoptric to the
dioptric system, and a committee of the Royal Society of Edinburgh met
at Dunbar, a distance of thirteen miles from the lighthouse, to make
observations on the two lights, which were exhibited in contrast. In
their report they conclude:--

'1. That at a distance of thirteen miles the mean effect of the new
light is very much superior to the mean effect of the old light
(perhaps in the ratio of two to one). 2. That at _all_ distances the
new light has a prodigious superiority to the old, from the equality
of its effects in all azimuths. 3. That the new light fulfils
rigorously the conditions required for the distribution of light to
the greatest advantage. 4. That at distances much exceeding thirteen
miles, the new light must still be a very effective one, though to
what extent the committee have not observed. The light is understood
to be still a good one, when seen from Edinburgh at a distance of
about thirty miles.'

On a further comparison of results, it was found that the light of one
of the great annular lenses, used in the revolving lights of the first
order, was equal to the united effect of about eight of the large
reflectors employed in the revolving lights on the Scottish coast. At
the Isle of May and Inchkeith the quantity of sperm-oil consumed by
the great lamp is equal to that burned by fourteen of the Argand lamps
used in the Scotch lights. Hence by dioptric means the consumption of
oil necessary for the fourteen reflectors will produce almost as
powerful a light as that which would require the oil of twenty-four
reflectors in the catoptric system, and consequently there is an
excess of oil equal to that consumed by ten reflectors, or four
hundred gallons in the year against the Scotch system.

The Dutch were the first to adopt Fresnel's system. In the year 1834
the Commissioners of Northern Lighthouses sent Mr. Alan Stevenson to
Paris to inspect the system, and his report was so favourable, that
the reflecting apparatus of the revolving light at Inchkeith was
removed, and the dioptric instruments substituted. The new light was
exhibited on the evening of the 1st of October, 1835, and so great was
the satisfaction afforded, that a similar change was made at the fixed
light of the Isle of May. The Tri