of Edinburgh, Session 1885 - 86 . 
497 
Electric Light. — The mean candle power of the electric arc given 
by one of De Meriten’s machines, in a lamp with 40 mm. carbons, 
was found by Messrs Dixon and Harcourt to be 10,000 candles. It 
was found that the core carbons gave a better result than the solid 
carbons ; also that two machines coupled do not give double the light 
of one ; this result, according to the report of Professor Grylls Adams 
of Cambridge, was however due to the electric energy being ex- 
pended in heating some of the “ leads,” which were of too small 
size. A considerable waste was also due to the regulator of the 
lamp. 
Gas Burners. — The Wigham gas burners experimented with 
varied from 108 jets down to 28 jets, and from 2300 to 250 
candle power ; while the Douglass Argand gas burners varied from 
6 to 10 rings, and their powers varied from 825 candle power to 
2500. 
Oil Burners. — The 6-wick Douglass oil burner was found to give 
730 candle power, while another of similar construction with 
9 wicks gave 1785 candle power. 
These results show how successfully the effectiveness of light- 
house burners has been lately increased through the efforts of Mr 
Wigham and Sir James Douglass. 
Variations in the Transparency of the Atmosphere. — Very remark- 
able variations in the transparency of the atmosphere were found to 
occur in the course of the observations, without any haze or fog or 
cloud being visible to the eye. Sometimes the experimental lights 
suffered a loss of J to J of their power, when inspected at a distance 
of a mile and a quarter ; while the Drench lights on the other side of 
the Channel, 25 and 30 miles distant, continued to show with 
their usual steadiness and brilliancy without any variation. 
The lenses employed in connection with the burners, which I 
have described were of two forms : — 
1. The Mew Island lens, which is an ordinary Fresnel lens of 
the first order, 920 mm. focal distance. 
2. The type employed at the New Eddystone Lighthouse, having 
the same focal distance, but with the addition of flint glass prisms 
above and below the central lens, so as to intercept a larger number 
of rays coming from the burner. 
So far as the experiments at the South Foreland dealt with the 
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