Wicuam—The Power of Continuous Lighthouse Lights. 349 
observed that when, after an interval of darkness, the light re- 
appears, it always seems to do so at a place different to that from 
which it had disappeared. This is due, of course, to the insensible 
wandering of the eye during the time of darkness. 
The apparatus is composed of 8 annular lenses of 45° each; 
the octagonal figure which they make is rotated at a speed of two 
seconds for each complete revolution. The impression produced 
on the retina by the flash from one lens remains until replaced by 
the flash of the next, and consequently a continuous pulsating 
effect is produced. Thus, it not only fulfils the conditions to 
which I have referred, but constitutes a light of an entirely new 
characteristic appearance, well calculated to arrest the attention 
of the mariner by its continual pulsation. 
I will now briefly bring under your notice another example of 
the usefulness for lighthouse purposes of the principle of which we 
have been speaking, viz. the capacity of the eye to receive the 
impression of a light if presented to it for a time so short as one- 
tenth of a second. This application has nothing to do with lenses, 
but consists simply in the rapid extinction and re-ignition of the 
light of a gas-burner. If, instead of extinguishing and re- 
igniting the light at intervals of about two seconds, as is done 
in the group-flashing lights at Galley Head, Mew Island, and 
Tory Island, we cause the extinctions and re-ignitions to succeed 
each other with great rapidity we produce the effect of a con- 
_ tinuous light, a light which never leaves the eye, and yet produces 
upon the retina a fluctuating effect, which is another of the dis- 
tinctive characteristics to which I have referred. When this is 
combined with the lenticular apparatus above described, the effect 
is very striking. The light is always visible, with its character- 
istic shudder, and further, it must not be forgotten (in these 
economic days), that in this case half the illuminant is practically 
saved. Indeed, neither of these devices for increasing the 
efficiency of lighthouse illumination is costly in application, 
and, at comparatively little expense, existing lighthouses may be 
altered to receive these improvements without the addition of 
expensive apparatus, so that the objection which is frequently 
raised by lighthouse authorities, that there is no money to spare 
for lighthouse improvement, does not hold good in this case. It 
may, therefore, be reasonably hoped that lights on this principle 
