20 ELECTRIC LIGHTING. 



" 3. The consumption of the carbons in the smallest pattern 

 of the lamps did not exceed 2 inches an hour, and for the large 

 pattern 3 inches. A length of one metre might be used. They 

 were Carre carbons." 



With this system, and for that matter with Reynier's system 

 also, all the lamps could be lighted or extinguished at once 

 or successively ; and as their brilliancy cannot be great, trans- 

 parent instead of ground glass globes may be used. 



Fig. 58 shows the commutators in each derivation, for 

 throwing into it the resistance a', for the interruption of the 

 circuit, and for direc f transmission ; they are metallic rings, 



FIG. 58. 



divided into 4 segments, within which is placed a plug half 

 of metal and half of an insulating substance. The two upper 

 parts of each ring are connected, one with the lower carbon 

 of the lamp, the other with the upper carbon ; but the con- 

 nection in the last instance is effected through a resistance 

 equal to that of the lamp, or 0*392 ohm. The lower part 

 on the left is connected with the positive wire, and the lower 

 part on the right is made of ebonite. When the plug is in 

 the first position shown in the figure, the current traverses the 

 lamp directly, because the communication is established by 

 the metallic part between the two metallic sectors at the 

 left ; when it is in the second position, the current no longer 

 passes through the carbons but through the resistance coil; 

 and as this is equivalent to that of the lamp, there is no change 

 in the distribution of electricity. Finally, when the plug is 



