THE ELECTRIC LIGHT. 437 



in standard candles the performance of the respective 

 machines : l 



Minimum. 

 1,523 

 1,953 

 4,016 

 4,016 

 8,932 

 3,339 

 4,138 

 2,811 



Two Gramme's (Nos. land 2) 11,396 6,869 



Two Siemens' (Nos. 1 and 2) 14,134 8,520 



These determinations were made with extreme care 

 and accuracy by Mr. Douglass, the engineer-in-chief, 

 and Mr. Ayres, the assistant engineer of the Trinity 

 House. It is practically impossible to compare photo- 

 metrically and directly the flame of the candle with 

 these sun-like lights. A light of intermediate intensity 

 that of the six-wick Trinity oil lamp was therefore 

 in the first instance compared with the electric light. 

 The candle power of the oil lamp being afterwards 

 determined, the intensity of the electric light became 

 known. The numbers given in the table prove the 

 superiority of the Alliance machine over that of Holmes. 

 They prove the great superiority both of the Gramme 

 machine and of- the small Siemens machine over 

 the Alliance. The large Siemens machine is shown to 

 yield a light far exceeding all the others, while the 



1 Observations from the sea on the night of November 21, 1876, 

 made the Gramme and small Siemens practically equal to the 

 Alliance. But the photometric observations, in which the external 

 resistance was abolished, and previous to which the light-keepers 

 had become more skilled in the management of the direct current, 

 showed the differences recorded in the table. A. close inspection 

 of these powerful lights nt the South Foreland caused my face to 

 peel, as if it had been irritated by an Alpine sun. 



