THE ELECTRIC LIGHT. 673 



The following table gives in standard candles the perform- 

 ance of the respective machines: * 



Name of Machines. Maximums. Minimum. 



Holmes 1,523 1,523 



Alliance . . . . . 1,953 1,953 



Gramme (No. 1) . . 6,663 4,016 



Gramme (No. 2) . 

 Siemens (Large) 

 Siemens (Small, No. 1) 

 Siemens (Small, No. 2) 

 Two Holmes' coupled 

 Two Gramme's (Nos. 1 and 2) 

 Two Siemens' (Nos. 1 and 2) 



6,663 4,016 



14,818 8,932 



5,539 3,339 



6,864 4,138 



2,811 2,811 



11,396 6,869 



14,134 8,520 



These determinations were made with extreme care and 

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

 Ay res, the assistant engineer of the Trinity House. It is 

 practically impossible to compare photometrically and 

 directly the flame of the candle with these sunlike lights. 

 A light of intermediate intensity that of the six- wick 

 Trinity oil lamp was therefore in the first instance com- 

 pared with the electric light. The candle power of the oil 

 lamp being afterward 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 

 coupling of two Grammes, or of two Siemens together, 

 here effected for the first time, was followed by a very 

 great augmentation of the light, rising in the one case 

 from 6,663 candles to 11,396, and in the other case from 

 6,864 candles to 14,134. Where the arc is single and the 

 external resistance small, great advantages attach to the 

 Siemens light. After this contest, which was conducted 



* 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 at the South Foreland caused my face to peel, as if it 

 had been irritated by an Alpine sun. 



