PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 575 



a vertical series of circular clusters, at a height of 264 feet from the 

 floor ; this is not yet illuminated. Total number of burners, 710. 



One level of, and appertaining to each tier is a gas stop-cock, 

 which is worked by an electro-magnetic engine in its vicinity, the 

 power being derived from the battery. 



The wire used is No, 10 copper wire, wound with linen thread 

 and covered with india rubber tubing, secretly laid through the 

 walls or covered from sight. The amount used is about five miles 

 in length, and the return circuit is made through the gas pipes. 



All the manipulations are performed by the operator in a pas- 

 sage way a few feet from the floor of the rotunda, who stands in 

 front of a dial plate which has eleven keys. 



The central key has two manipulations — one makes the battery 

 connection, and the other brings any number of the sections of the 

 battery into play, the range being from 20 to 200 jars. The ten 

 keys which are ranged around the centre arc for the gas and light- 

 ing connections of the respective tiers, of which three are in opera- 

 tion — one at the spring of the dome not yet made, and the tholus 

 at the height of 84 feet above the eye of the dome, 264 feet from 

 the floor of the rotunda. 



The gas key appertaining to each tier has a dark and a light 

 segment attached to it, which, showing through the orifices in the 

 face-plate, indicates when the gas is off or on, and the motion of 

 bringing the light segment to view makes a series of electrical 

 connections with the electro-magnectic engine, which operates as 

 the gas stop-cock. 



The lighting key, in like manner, in its revolution, makes a series 

 of battery connections with circuits, which embrace sections of the 

 circle of burners. The burners, which are from six to twelve 

 inches apart, are arranged in sections of thirty or more, each sec- 

 tion having an independent circuit connection with the battery 

 under the control of operator at the dial phite, who, by the revo- 

 lution of the key, makes the series of connections to the consecu- 

 tive sections in the tier of burners. This serial character is 

 designed to obviate the escape of gas, which would take place 

 were the gas allowed to extend all around the circle before any of 

 the burners were lighted, as it would commence escaping at the 

 burners nearest its entrance, and would be very sensibly present 

 before it had reached the other side of the circle of one hundred 

 feet diameter. The aim of the present arrangement is to follow 

 the gas influx with an electric connection, which lights the gas 



