496 
Proceedings of the Royal Society 
2. “ That for all practical purposes the gas light, as exemplified 
hy Mr Wigham’s multiform system, and the oil light, as exemplified 
by the Trinity House Douglass 6-wick burners, in multiform 
arrangement up to triform when shown through revolving lenses are 
equal, light for light, in all conditions of weather ; but that quadri- 
form gas is a little better than triform oil.” 
3. “ That when shown through fixed lenses, as arranged in the 
experimental towers, the superiority of the super-posed gas light 
is unquestionable. The larger diameter of the gas flames, and the 
lights being much nearer to each other in the gas lantern, give the 
beam a more compact and intense appearance than that issuing from 
the more widely separated oil burners.” 
4. “That for lighthouse illumination with gas, the Douglass 
patent gas burners are much more efficient and economical than the 
Wigham gas burners.” 
5. “ That for the ordinary necessities of lighthouse illumination, 
mineral oil is the most suitable and economical illuminant, and that 
for salient headlands, important ’landfalls, and places where a very 
powerful light is required, electricity offers the greatest advantages.” 
There were employed during these experiments a variety of forms 
of photometer, but the most important was the Pentane standard 
photometer, the invention of Mr Yetnon Harcourt, which was 
recommended to the Board of Trade, as giving the most uniform 
standard of comparison, by Professors Williamson and Odling, and 
Mr Livesey of London ; while for outdoor observation, there was 
used a liquid photometer, consisting of a water-tight telescope, filled 
with a partially opaque fluid, supplied to the telescope from a small 
cistern fixed above, so that as the eyepiece is moved out or in, the 
length of the fluid through which the light has to pass increases or 
diminishes, and the length of the fluid through which the light so 
passes, is recorded by an attached graduated scale. This form of 
photometer was first proposed by me in the Edinburgh New Phil. 
Journal in 1863, and has since been employed in numerous experi- 
ments on lighthouse apparatus at Edinburgh. 
The South Eoreland experiments extended over a period of 
twelve months, and many interesting observations were made, besides 
those which related to the questions which were the more immediate 
cause of the investigations being instituted. 
