82 DYNAMO-ELECTRIC MACHINES. 



there was no fear, even with a continually increased annual output, for 

 the next iooo years at least. Although heat is inseparably connected 

 with all mechanical motion, it is of but secondary importance as 

 compared with light. No operation could possibly be carried on 

 without the aid of light. Light infuses life and vitality into every 

 living organism. It is essential to life. Our very thoughts are 

 dependent upon it, for by its aid through our senses, the brain re- 

 ceives impressions from without, which suggest new ideas and 

 consequently thought. It permeates everything, and the more light 

 that is thrown upon any subject, both figuratively and literally, the 

 more it becomes evident to our senses, and the more easy to com- 

 prehend. 



Since the general introducton of power in the manufacture of 

 textile fabrics occured, now, about a century ago, artificial light be- 

 came a necessity. This was owing to two causes; first, because of the 

 extent of such operations, and secondly, because of the increased 

 demand, owing to the lessened cost of production. The decreased 

 cost of production, and the consequent increased demand, necessi- 

 tated the building of large factories, which in turn required a greater 

 supply of artificial light. This was met by a supply of gas, which 

 had its advent about the beginning of the present century. A great 

 impetus was then given to all industrial operations, as work which 

 was formerly restricted to daylight could then be carried on at night; 

 the imperfect light obtained from the burning of oil lamps, which 

 were then used, limitii g such operations. About seventy-five years 

 ago, Davy experimer ted with batteries of various powers for the 

 production of luminous sparks, and these were continued until he 

 reached the number of 2000 cells when he not only obtained sparks 

 of great length, but a continuous light, by passing the electric current 

 through two pieces of charcoal. The carbons were held horizontally, 

 which caused an arched form to be assumed by the light, and hence 

 the name of arc light. The name is used to-day chiefly to distinguish 

 it from light by incandescence. 



The principle of induction upon which Dynamo Electric Machines 

 are based, was discovered by Michael Faraday, to whom the world is 

 largely indebted, for without his discovery, electric generators by 

 power alone, could not to-day be in existence. This discovery was 

 made about 1830, since which time many efforts have made by 



