592 THE POPULAR SCIENCE MONTHLY. 



electric current Las ever before been conducted for a similar purpose. 

 The signalling apparatus is placed in a lantern five feet high, four feet 

 wide, and having a semicircular glazed front, which projects from the 

 lantern of the belfry on the north side of the tower, or that overlooking 

 the Victoria Embankment. It consists first, of a fixed table, in which 

 is inserted a fiat brass ring 16 inches diameter and one inch broad, 

 which serves as a roller-path for the apparatus carrying the lamp and 

 reflector; next, there is a circular revolving table, having bearings on 

 the roller-path, and which is moved around a central pivot projecting 

 from the fixed table, being actuated by a worm wheel and screw. By 

 means of this arrangement the light can be directed horizontally from 

 side to side through an arc of 180. It could, of course, be made to 

 sweep the whole of the horizon, but the position of the lantern with 

 regard to the clock-tower is such as to enable the light to be seen 

 through the range of a semicircle only. Upon the revolving table, 

 and hinged to it at the front, is the elevating table, which has a screw 

 adjustment to the rear by which the light can be raised or depressed, 

 being capable of vertical training through an arc of 25. On the ele- 

 vator is placed the lamp-table, upon which again is a sliding platform, 

 on which the lamps themselves stand. There are two lamps, which 

 are in use alternately, the carbon-points lasting but four hours, while 

 the House frequently sits for ten. 



The copper conductors terminate at the fixed part of the machine, 

 and the method of carrying the current from them to the lamps is 

 very ingenious, the moving parts of the apparatus forming in them- 

 selves conductors. The negative conductor is placed in metallic con- 

 tact with one hinge of the elevator-table through the centre-pin on 

 which the table revolves, and the positive conductor with the other 

 hinge by means of the brass roller-path. The currents from those 

 points are conducted to the lamp-table, and thence through the 

 traversing platform to the lamps, metallic contact being obtained 

 throughout the whole circuit by means of flat springs moving over 

 flat surfaces. The changing of the lamps is effected, without any ap- 

 preciable break of continuity in the light, by means of the traversing 

 platform on which they stand, and which has a sliding motion from 

 side to side. When the carbon-points in one lamp are nearly con- 

 sumed, the traverser is quickly shifted from right to left, or vice versa, 

 as may be necessary. The break of contact is but momentary, and 

 only exists during the time required to move the traverser rapidly 

 through a space of six inches. The light will not become extinct dur- 

 ing that period, as there is not sufficient time to allow the incandes- 

 cence of the carbon to entirely subside. The springs under the lamp 

 thrown out of use are by this action removed from the metal plate in 

 the lamp-table, and the springs under the fresh lamp are brought into 

 contact, and the light is at once produced anew. 



The intensifying apparatus at present in use is a holophole lent by 



