682 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



preparation of the sulphuric acid solution as well as for the zinc 

 amalgams necessary to put the system of batteries in action. 



At the right corner of the electric room is a large reservoir, of the 

 capacity of about one cubic metre, where water mixed with one-tenth 

 of sulphuric acid can be stored. A spigot permits this liquid to run 

 into a vertical siphon formed of a large tube, into which an areometer 

 is plunged to ascertain its quality, and make sure that the preparation 

 has been made in the proper proportions. The reservoir is furnished 

 at its lower part with an earthenware pipe, which is conducted along 

 the walls of the room opposite the six-battery tables. Beside each 

 table an earthenware spigot enables the operators to run the liquid 

 into earthenware jugs, from which the battery -jars are filled with the 

 liquid. 



M. Dubosq has obviated the dangerous action of the nitrous 

 vapours by placing here and there upon the piles saucers containing 

 ammonia, which condenses them. 



The electric wires are conducted along the wall ab the bottom of 

 the room, where they traverse six galvanometers (Plate XX.). Each 

 of these galvanometers indicates, by means of the needle with which it 

 is provided, the condition of the battery to which it corresponds. The 

 six insulating wires, after leaving the six galvanometers, pass along the 

 walls to the stage, where the currents which they carry may be 

 utilised either singly or by twos or threes, according to the degree of 

 intensity which it is wished to give to the light. The distance which 

 the current runs from the electric room to the most distant point of 

 the stage is about 122 metres; the total length of all the wires is 

 about 1,200 metres. 



M. Dubosq, imitating the system of telegraphic wires, makes use 

 of the earth as a return current ; one of the poles of each battery is in 

 communication with the iron of the building. Without this arrange- 

 ment it would have been necessary to double the length of the wires. 



In most instances M. Dubosq places his electric lamp on one of 

 the wooden galleries which run along the higher regions of the 

 scenery above the stage. It is from this artificial sky that he darts 

 upon the ballet the rays of his electric sun, or, decomposing the light 

 by means of the vapour of water, he throws upon the stage a veritable 

 rainbow, as in Moses ; again, it is thus that he causes the light from 

 the painted windows to fall upon the flags of the church where 



