24 Illumination of Beacons and Buoys.  [January, 
being raised to incandescence are gradually consumed; and 
this consumption is the weak point of the system, necessi- 
tating a delicate automatic arrangement to maintain a con- 
stant distance between the points. Of the merit of the 
light evolved, Mr. Stevenson says :—‘‘ Through the kind- 
ness of the Elder Brethren of the Trinity House, I had an 
opportunity of inspecting Dungeness Light after nightfall, at 
different distances. The weather being very favourable, 
there was an excellent opportunity of viewing it, and the 
French revolving light of Grisnez on the opposite coast. 
The result was upon the whole very satisfactory ; the Dun- 
geness sixth-order light, though showing continuously all 
round the horizon, contrasted well with the revolving, and 
therefore, more concentrated and first-class (oil) light of 
Grisnez, when viewed from a distance of about twelve 
miles. The electric light was generally very effective and 
striking in its appearance, though it frequently fell off, 
suffering prodigiously in volume; and once or twice it 
disappeared altogether for a second or two. This temporary 
extinction, though no doubt an evil, is not, from its very 
short continuance, a practical defect of any importance.” 
But there is the important fact to be observed that the 
electric light appears to possess less power to penetrate the 
atmosphere than does the oil light. ‘‘ When viewed from 
Dover, a distance of about eighteen miles,” says Mr. W. 
Stevenson, ‘‘the result was decidedly in favour of Cape 
Grisnez.” Still this loss of penetration could be com- 
pensated by increasing the original power; while it should 
be remembered that the order of the lamps differed greatly. 
Electric lamps for lighthouse purposes, moreover, are generally 
of too small dimensions, and hence, as the angle of diver- 
gence of the rays within the apparatus must be larger, any 
variation of the carbon-points from the true focus will give 
rise to a more extensive displacement of the emergent rays 
than would be the case with lamps of the size used for the 
oil light. In furtherance of this view, Messrs. Stevenson, 
in their Report of November 27th, 1865, to the Northern 
Lighthouses, recommended the adoption of apparatus of the 
third and fourth orders as being preferable to that of the 
sixth. This would entail some alteration in the form of the 
lenses in order to produce a greater amount of vertical 
divergence. 
The penetrating power of the electric light is not, how- 
ever, a question that need be raised in its application 
to the illumination of buoys and similar surface sea-marks ; 
for it is generally sufficient that their light should be seen at 
