LIEUT. DRUMMOND ON THE ILLUMINATION OF LIGHT-HOUSES. 391 
These results were obtained by screening the different lights, and then 
placing equal apertures opposite each, changing the apertures and taking the 
mean to destroy the effect of any inaccuracy in size. The intensity of the 
lime-ball being therefore 264 times that of the Argand lamp, a single reflector 
illuminated by the former will be equal to 264 reflectors illuminated by the 
latter ; but the divergence of the reflected light, depending upon the size of the 
luminous body in the focus, will be smaller with the ball than with the lamp in 
the proportion of about 3 to 8 : hence in such a light-house as that of Beachy 
Head, 8 reflectors may be substituted for 30, and yet an effect would be pro- 
duced 26 times greater than that of the present light, the most perfect of its 
kind in this country. 
By similar experiments it was found that the French lens was equal to 9.1 
reflectors; and if the effect of the additional lenses and reflectors which ought to 
accompany it, and which has been estimated at one-seventh, be added, then the 
lens is equal to 10.4 reflectors. In like manner, therefore, the effect of a single 
reflector with a lime-ball would be equal to 25 times that of such a combination 
of lenses. 
Such appear to be the singular and important results of our late experiments 
at the Trinity House, made as they have been with every precaution by diffe- 
rent individuals, with different instruments, and unbiassed by the knowledge 
of each other’s results. I see no reason to doubt their accuracy ; and the com- 
parative appearances of these different lights, when exhibited at a distance of ten 
miles, to which I shall presently allude, though not admitting of being reduced 
to numbers, confirm the striking superiority of this method of illumination. 
It may now perhaps be asked. At what expense can such a light be main- 
tained ? Can the gases by which the requisite heat is produced be procured at 
such a price as to compete with oil or coal gas ? The data I possess for form- 
ing an estimate of the expense of the gases are very scanty, but the quantity 
consumed was accurately determined ; at the same time the consumption of 
the other lights was also tried, and the results are as follow : 
An Argand lamp seven-eighths of I 
an inch in diameter . ... f 
The same placed in a reflector . . 
The French lamp 
Consumption 
in hours. 
1 gill . . . 
H gill • 
2 qts. \ pt. . 
Expense 
per hour. 
0.69 penny 
0.83 penny 
Is. 2\d. 
3 E 
MDCCCXXX. 
