54 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



impossible to make 220-volt lamps, and though they are now available, 

 their use is uneconomical, as their efficiency is much poorer than that 

 of iio-volt incandescent lamps. 



Edison invented a distributing system that had tw^o iio-volt circuits, 

 with one wire called the neutral, common to both circuits so that the 

 pressure on the two outside wires was 220 volts. The neutral wire 

 had only to be large enough to carry the difference between the cur- 

 rents flowing in the two circuits. As the load could be so arranged 

 that it would be approximately ec^ual at all times on both circuits, 

 the neutral wire could be relatively small in size. Thus the three-wire 

 system resulted in a saving of 60 per cent in copper over the two-wire 



Diagram of Edison's Thrke-Wire System, 1 



This system reduced the cost of copper in the multiple distributing 

 system 60 per cent. 



system or, for the same amount of copper, the distance that current 

 could be delivered was more than doubled. 



DEVELOPMENT OF THE ALTERNATING CURRENT CONSTANT 

 POTENTIAL SYSTEM 



The distance that current can be economically distributed, as has 

 been shown, depends upon the voltage used. If, therefore, current 

 could be sent out at a high voltage and the pressure brought down to 

 that desired at the various points to which it is distributed, such dis- 

 tribution could cover a much greater area. Lucien Gaulard was a 

 French inventor and was backed by an Englishman named John D. 

 Gibbs. About 1882 they patented a series alternating-current system 

 of distribution. They had invented what is now called a transformer 

 which consisted of two separate coils of wire mounted on an iron 



