686 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



kind dates from the reconstruction of the Notre Dame bridge at Paris. 

 Since then the electric light has been made use of in the construction 

 at the Louvre and the bridge of Kehl. 



The electric light has also been employed upon the Clock Tower 

 of the Houses of Parliament in London, as a signal light to show to 

 members outside by its illumination that the House is still sitting. 

 The source of electricity in this case was the dynamo- electric 

 machine of M. Gramme. 



The machine employed was driven by a two-horse-power engine 

 at a speed of 320 revolutions per minute, and produced a light equal 

 to 7,000 sperm candles at a cost of about one shilling per hour. The 

 machine was placed in the basement of the building, and was connected 

 with the optical apparatus at the top of the tower by thick copper 

 wires, through a distance of 900 feet. 



As the extinction of the light indicates the adjournment of the 

 House, it became of paramount importance to insure the absolute 

 continuity of the light, and as the longest carbons last only about five 

 hours, and the House frequently sits for ten, a special apparatus had 

 to be employed, which was designed by Mr. Conrad Cooke, under 

 whose directions these experiments were conducted. Two Serrin 

 regulators are carried side by side upon a miniature trolley, underneath 

 which are two sets of copper springs, so adjusted that when one lamp 

 is in position in the focus of the optical apparatus, its corresponding 

 springs are in metallic contact with two studs, which are the terminals 

 of the wires leading from the machine. The lamp is by that means 

 thrown into the circuit and the lio;ht is established. When the car- 



O 



bons are nearly consumed the trolley is quickly shifted from right to 

 left, or vice versa, and the springs of the second lamp come into contact 

 as the others are run off. The break of continuity is but momentary, 

 but this does not affect the light, as the time is too short for the 

 incandescence of the carbons to subside. 



Other less successful attempts have been made to use it for 

 the public illumination of large towns. It was first attempted 

 to replace the numerous gas-lights in the squares, quays, and 

 streets by a powerful electric-light, the rays of which were thrown 

 by reflectors over the whole space to be illuminated. The effect 

 was brilliant, but disastrous, and for this reason. The electric-light 

 is distinguished by an extreme intensity, but for this very reason its 



