672 FRAGMENTS OF SCIENCE. 



electric lamp be introduced into the common circuit of 

 magnet and armature, we can readily obtain a most power- 

 ful light.* By this discovery, then, we are enabled to 

 avoid the trouble and expense involved in the employment 

 of permanent magnets; we are also enabled to drop the 

 exciting magneto-electric machine, and the duplication of 

 the electro-magnets. By it, in short, the electric generator 

 is so far simplified, and reduced in cost, as to enable elec- 

 tricity to enter the lists as the rival of our present means of 

 illumination. 



Soon after the announcement of their discovery by 

 Siemens and Wheatstone, Mr. Holmes, at the instance of 

 the Elder Brethren of the Trinity House, endeavored to 

 turn this discovery to account for lighthouse purposes. 

 Already, in the spring of 1869, he had constructed a 

 machine which, though hampered with defects, exhibited 

 extraordinary power. The light was developed in the 

 focus of a dioptric apparatus placed on the Trinity Wharf 

 at Black wall, and witnessed by the Elder Brethren, Mr. 

 Douglass, and myself, from an observatory at Charlton, on 

 the opposite side of the Thames. Falling upon the 

 suspended haze, the light illuminated the atmosphere for 

 miles all round. Anything so sunlike in splendor had not, 

 I imagine, been previously witnessed. The 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 previously 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 machines 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; 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. 



* In 1867 Mr. Ladd introduced the modification of dividing the 

 armature into two separate coils, one of which fed the electro- magnets, 

 svhile the other yielded the induced currents. 



