observation of distant stations in geod&tical operations. 337 
not be considered too dearly purchased at such a price. 
Whether it would be most advantageous to collect the light 
with common parabolic reflectors, or to adopt the system of 
lenses and plane reflectors, proposed by M. Fresnel, with 
such modifications as the peculiar nature of the light might 
admit or require, would readily be determined by experiment 
There are good grounds for believing that this latter mode 
would be found the most economical and effective ; and that 
a light-house might be brilliantly illuminated by a single ball 
of lime ; in which case the expense would not exceed, if it 
equalled that of oil. It might not be uninteresting at the 
same time, to enquire what degree of light could be obtained 
from lime, by employing atmospheric air with common oil or 
tallow, as the source of heat. From some rough experiments 
made with this view, it seemed not improbable that it would 
possess considerable superiority over that of an argand lamp. 
But whatever might be the result of these enquiries, it will 
probably be admitted that enough has already been prac- 
tically carried into effect, to show that no formidable diffi- 
culty stands in the way of the application of this mode of illu- 
mination to light-houses, and that the subject is not unde- 
serving the attention of those, to whose charge these important 
establishments are committed. 
