IMPROVEMENTS IN PHAROLOGY. 167 
section G of the British Association, at its meeting recently 
held at Leeds, and it at once occurred to me that the prin- 
ciple of gyration might be advantageously applied to neu- 
tralize the powerful action of the wind and waves upon 
floating light-beacons. I have since then given some at- 
tention to the subject, and have embodied my ideas in the 
diagram which I have now the honour to submit to the 
Society. 
Before describing my proposed improvements it will be 
necessary, for the sake of perspicuity, briefly to consider 
the two systems now in use for the illumination of light- 
houses, viz: the catoptric or English system, which con- 
sists in the use of many lamps with metallic reflectors 
placed behind the lights, and the dioptric or lenticular 
system, which consists of a number of lenses united or built 
up so as to form a vertical octagonal hollow prism; which, 
circulating around a single light fixed in the centre, shows 
to a distant observer successive flashes or blazes of light 
whenever one of its faces crosses a line joining his eye and 
the lamp. The invention of this system is, I believe, due 
to the late Mons. Augustin Fresnel, whose name it bears. 
The object to be attained by the use of both these sys- 
tems is of course the same, namely, to collect the rays of 
light which diverge from a point called the focus, and to 
project them forward in a beam whose axis coincides with 
the produced axis of the instrument; but the means 
whereby they attain this end are different, this result being 
produced in the catoptric system by the light being re- 
flected or thrown back from a surface so formed as to cause 
all the rays to proceed in one and the same direction ; 
whilst in the dioptric system they pass through the refract- 
ing medium and are bent or refracted from their natural 
course into that which it is desired they should take. It 
is impossible by any combination of paraboloidal reflectors 
to distribute around the horizon a zone of light of equal 
