499 
of Edinburgh, Session 1885 - 86 . 
apparatus, and by exact photometric observations made by Mr 
Dixon, of which the following are the results : — 
Time. 
No. of Burner. 
Lens. 
Illuminating 
Power in 
Pyres or 1000 
Candles. 
Rate of 
Gas 
Consump- 
tion. 
7.30 
I. 108 Gas 
Mew Island 
22-8 
300 
7.40 
I. 6-wick Oil 
Stevenson 
29-3 
7.48 
I. 108 Gas 
Mew Island 
23-4 
300 
7.55 
I. 6-wick Oil 
Eddystone 
18-1 
8. 
II. 108 Gas 
Mew Island 
. 41-6 
298 
8.8 
I. 10-ring Gas 
Eddystone 
31-8 
225 
8.15 
I. 10-ring Gas 
Stevenson 
62-2 
8.20 
II. 108 Gas 
Mew Island 
43-2 
298 
8.25 
High Light 
7-6 
8.30 
I. 108 Gas 
Mew Island 
23-1 
310 
8.35 
I. 6-ring Gas 
Stevenson 
28-9 
100 
8.50 
I. 6-ring Gas 
Eddystone 
13-7 
110 
8.55 
I. 108 Gas 
Mew Island 
21- 
310 
9.15 
I. 108 Gas 
Mew Island 
22*4 
310 
9.20 
I. 108 Gas 
Stevenson 
42-6 
330 
9.25 
I. 108 Gas 
Mew Island 
22-4 
310 
The following conclusions from these photometrical trials seem 
warranted : — 
1. That a single large burner shown in a complete panel of a 
revolving apparatus composed of the new lens, with totally reflecting 
top and bottom prisms of corresponding size added, would give a 
more intense light than burners and ordinary Fresnel lenses, 
arranged as biform and equal to triform. 
2. That the consumpt of oil or gas would be a J, J, and J of that 
of biform, triform, or quadriform arrangements respectively. 
3. That the new lens apparatus would avoid all the disadvantages 
of superposed lenses, including excessive heat in the lightroom, 
difficulty of management of the burners, and obstruction of light by 
the necessary ventilating tubes. 
The practical result is obvious, that for lighthouse purposes, on 
the grounds of superior illuminating power, economy and ease of 
management, the principle of increasing the diameter of the apparatus 
in proportion to the size of the burner, is superior to that of super- 
posing lenses and burners ; in a word, that the new lens apparatus 
is superior to the biform, triform, and quadriform arrangements. 
The trials at the South Foreland were made with apparatus in 
existence at the time when the experiments were instituted, and I 
have since proposed to take advantage of the natural properties of the 
