562 THE POPULAR SCIENCE MONTHLY. 



apparatus of Holmes, however, was rapidly distanced by the safer and 

 more powerful machines of Siemens and Gramme. 



As regards lighthouse illumination, the next step forward was taken 

 by the Elder Brethren of the Trinity House in 1876-77. Having pre- 

 viously decided on the establishment of the electric light at the Lizard 

 in Cornwall, they instituted at the time referred to an elaborate series 

 of comparative experiments wherein the machinery of Holmes, of the 

 Alliance Company, of Siemens, and of Gramme, were pitted against 

 each other. The Siemens and the Gramme machines delivered direct 

 currents, while those of Holmes and the Alliance Company delivered 

 alternating currents. The light of the latter was of the same intensity 

 in all azimuths round the place of observation ; that of the former was 

 different in different azimuths, the discharge being so regulated as to 

 yield a gush of light of special intensity in one direction. The follow- 

 ing table gives in standard candles the performance of the respective 

 machines : ' 



Name of Machines. Maximum. Minimum. 



Holmes 1,523 1,523 



Alliance 1,953 1,953 



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



" (No. 2) 6,663 4,016 



Siemens (large) 14,818 8,932 



" (small. No. 1) 5,359 3,339 



" (small. No. 2) 6,864 4,138 



Two Holmes's coupled 2,811 2,811 



Two Gramme's 11,396 6,869 



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



These determinations were made by Mr. Douglass, the engineer-in- 

 chief, and Mr. Ayres, the assistant engineer of the Trinity House. After 

 this contest, which was conducted throughout in the most amicable 

 manner, Siemens machines of the smaller type were chosen for the 

 Lizard.^ 



We have machines capable of sustaining a single light and also 

 machines capable of sustaining several lights. The Gramme machine, 

 for example, which ignites the Jablochkoff candles on the Thames Em- 

 bankment and at the Holborn Viaduct, delivers four currents, each 

 passing through its own circuit. In each circuit are five lamps through 

 which the current belonging to the circuit passes in succession. The 

 lights correspond to so many resisting spaces, over which, as already 

 explained, the current has to leap ; the force which accomplishes the 



' Observations from tlio sea on the night of Norember 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. 



' As the result of a recent trial by Mr. Schwendler, they have been also chosen for 

 India. 



