384 LIEUT. DRUMMOND ON THE ILLUMINATION OF LIGHT-HOUSES. 
and take part in a course of experiments instituted by order of the Trinity 
House, and carried on under the direction of the Committee for the Manage- 
ment of Light-houses, with a view to ascertain the relative merits of different 
methods either adopted or proposed to be adopted in the illumination of light- 
houses. The result of these experiments I have received permission to com- 
municate to the Royal Society ; but in order that the particular methods to 
which they refer may be better understood and more fully appreciated, a few 
preliminary observations may be necessary. 
The more rude and ancient methods of illuminating light-houses with open 
coal fires, with common lamps or candles, sometimes aided by reflectors com- 
posed of small facettes or plane mirrors*, have in this country been completely 
superseded even in light-houses of secondary importance ; and it may be said 
that there is only one method now in use for this purpose along the coast of 
Great Britain and Ireland. This consists in the use of a parabolic reflector of 
about three or four inches focal length, and from twenty-one to thirty inches in 
diameter, illuminated by an Argand lamp, seven-eighths of an inch in diameter, 
placed in the focus. The reflector is hammered out of a plane surface consist- 
ing of two plates of silver and copper rolled out together, and though executed 
with great skill, considering the means, cannot be regarded as a very perfect 
instrument. This description must be understood as applying only to light- 
houses under the management of public bodies : with respect to those which 
have been let to private individuals, I have no very accurate information ; 
but, if they should, on examination, prove to be of an inferior order, it would 
only be the natural consequence of so pernicious a system. 
In fixed lights the number of these reflectors varies according to the portion 
of the circumference required to be illuminated ; but it should not be less than 
this arc divided by the angle of divergence of the reflected light. At the 
Eddystone, where the whole circle requires to be illuminated, the number 
* The Eddystone till the year 1811 was lighted with 24 wax candles. Up to that time it was in 
the hands of private individuals; but on the expiration of the lease the Trinity House took it under 
their own management, and immediately substituted lamps and reflectors. The Bidstone, a leading 
light to Liverpool, consisted of a large built reflector, about 10 feet in diameter, lighted by an immense 
'.pout-lamp with a wick about 12 inches wide, from which a volume of smoke arose that completely 
intercepted the light from the upper part of the reflector. 
