494 
Proceedings of the Royal Society 
Monday , 4 th January 1886. 
THOMAS STEVENS OH, Esq., M.Inst.C.E., President, in 
the Chair. 
The following Communications were read : — 
1. Notes on Experiments for the Board of Trade, made at the 
South Foreland Lighthouse by the Trinity House of 
London, on Lighthouse Illuminants, &c. By Thomas 
Stevenson, Pres. B.S.E., M.Inst.C.E. 
A very important inquiry — suggested by Mr Chamberlain when 
President of the Board of Trade — has just been concluded by the 
Trinity House of London into the relative merits of electricity, gas, 
and oil, as lighthouse illuminants, on which I think it advisable to 
make a few remarks, as the general results of the investigation 
ought to possess a certain amount of interest for this Society. 
Mr Wigham, gas engineer, Dublin, has long taken a great interest 
in the best means of increasing the power of our sea lights by means 
of gas and large burners. So far back as 1865 he proposed to 
increase the diameter of gas burners to 7 inches; and in 1868, the 
Scotch Lighthouse Board was asked by the Board of Trade to 
investigate the subject. Certain experiments were accordingly 
made at Granton in that and the following year. In 1869 the 
engineers of the Northern Lighthouse Board reported in the follow- 
ing terms, on the results of the experiments which had been made 
on the employment of large burners 
“ It has been found that the second series of experiments so far 
corroborated those previously made as to leave no room for doubt 
that the gas light when used with ah annular lens, notwithstanding 
the greater size of the flame, was not superior to the effect of the 
smaller flame of the mechanical lamp, the explanation being that 
the greater portion of the large-sized 7-inch gas flame, consisting of 
52 jets, is ex-focal , and is therefore lost, so that with the lens no 
advantage is gained by increasing the size of the flame beyond 
certain limits, and these seem to be pretty nearly attained in the 
ordinary 4-wick lamps. So apparent was this, that with Mr 
Wigham’s concurrence, it was agreed to give up the idea of experi- 
menting on the gas burner in its present form as applicable to 
