Figure 14. — Current regulator and arc-light regulator of Lacassagne and Thiers. From 

 Bulletin de la Societe f Encouragement pour Plndustrie Nationale, 1857, vol. 4, pi. 1 13. 



unskilled workmen to handle. Moreover, even with 

 the best cells of the time, the power was such that the 

 light was appreciably reduced after several hours use. 

 If the light were to be maintained constant, a new 

 battery had to be switched into the circuit. In 

 addition, the cells were too bulky (at least 20 Bunsen 

 cells had to be used for each arc lamp) and too fragile 

 for any e.xtensive application to the industrial arts. 



There was a laboratory device oh hand, however, 

 that did not depend on the consumption of metals to 

 produce electrical power but, instead, transmuted 

 mechanical power into electrical. The reciprocal 

 relation between mechanical motion and electrical 

 current was discovered in the early 1830's, but almost 

 half a century passed before it was possible to apply 

 this knowledge to the commercial generation of 

 electrical power. Such an application did not become 

 possible until the device known as the dynamo was 

 invented, but simpler generators were well known in 

 the laboratory before that date. Once it had been 

 shown that these generators could be used to supply 

 power for illumination by electricity, a number of 

 inventors sought to bring them from the laboratory 

 into the field of commerce. This laboratory instru- 

 ment was based on Faraday's discovery of electro- 



magnetic induction, and we must briefly return to the 

 1 830's to discuss the development of the generator. 



Like Oersted, although for somewhat different 

 reasons, Michael Faraday felt that all the forces of 

 nature must be somehow related. In particular, if 

 a certain relation exists between two different forces, 

 the converse of that relation must also exist. Such 

 considerations led Faraday to seek an effect oppo.site 

 to that of Oersted — that of obtaining an electric 

 current from magnetism. He finally discovered it in 

 the relative motion of a magnet with respect to a 

 closed circuit (fig. 20). Investigation of the same 

 relation was pursued by Joseph Henry about the same 

 time, but his delay in publishing the results has tended 

 to obscure his contributions.^^ 



Mechanical devices that continuously transform 

 energy from a mechanical to an electrical form fol- 

 lowed within a few months of Faraday's discovery 

 of induction. One of the first such devices was 



21 Michael Faraday, "Experimental Researches in Elec- 

 tricity," Philosophical Transactions, 1832, vol 122, pp 125-162; 

 A. Fresnel, "Note sur des essais ayant pour but de decomposer 

 I'eau avec un aimant," Annates de chimie et de physique, 1820, 

 ser. 2, vol. 15, pp. 219-222; Joseph Henry, "On the Production 

 of Currents and Sparks of Electricity from Magnetism," 

 American Journal of Science, 1832, vol. 22, pp. 403-408. 



344 



BULLETIN 228: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



