336 Lieut. Drummond on the means of facilitating the 
would be sufficient for its management. Even on the survey 
this requires n j peculiar address, notwithstanding the inconve- 
niences of very exposed situations, and the necessity of render- 
ing every article as portable as possible. The expense may 
appear, at first sight, the strongest objection to its general 
use ; but, supposing rectified spirits to be employed, with the 
duty remitted, and no further use to be made of the oxide of 
manganese, after the abstraction of the oxygen,* it may be 
stated, in general terms, that while the intensity of light 
varies between 6 o and 90 times that of an argand lamp, the 
expense would not exceed ten times. Applied to a revolving 
light, where four sides are illuminated, each with four reflec- 
tors, one reflector, with the lime light, might be substituted 
on each side, and with an increased expense of times that 
of the oil an intensity varying between 15 and 22 would be 
obtained. It will also be recollected that the oil consumed 
is far from constituting the most considerable portion of the 
expense of maintaining a light-house, and that it would pro- 
bably not be underrated if estimated on an average at one- 
fourth. The other sources of expenditure would, in both 
cases, be the same. How far this increased expense would 
be an objection to its general introduction into light-houses, 
is for others to determine; but there are, I should apprehend, 
situations, such for example, as the Lizard Point, the Scilly 
Islands, or the great Skellig,-f off the south-west extremity of 
Ireland, where the advantages of so powerful a light would 
* It is not improbable that some simple process might be found for causing the 
manganese to absorb from the atmosphere the oxygen which it had lost by ex- 
posure to heat ; in this case the expense would be diminished about two-thirds. 
f A light-house is now building on this remarkable rock, which will be of great 
importance, being the first made by vessels from America. 
