170 THE AGE OF ELECTRICITY. 



inent. Light, then, would be a combination of electric currents, char- 

 acterized by the prodigious frequency of alternations, a billion during 

 a millionth of a second. Amj^ere could not foresee that the S])eculatious 

 of his imagination Avould so soon be put in so precise a form. 



Maxwell's theory, however, was not accepted without manj' reserva- 

 tions; it still lacked the confirmation of experiment, for the properties 

 of the dielectrics obey but in an imi^erfect manner the laws as indi- 

 cated. Hertz's experiments afforded a memorable confirmation. Thanks 

 to the discoveries of the inventor and the investigations of the physi- 

 cists who followed in his footsteps, the demonstration is now made that 

 the electric oscillations travel with the same velocity as light, that they 

 produce the same phenomena of interference, that they are subject to 

 the same laws of reflection and refraction; they could be iierceived by 

 the eye if it were possible to give them the same frequency. That 

 extreme limit is still far from being reached, since the shortest electric 

 undulations that have been observed are not less than several centi- 

 meters, that is, one hundred thousand times longer than those of light. 



So that all the phenomena which were at first ascribed to various 

 independent causes nuist now be explained by means of the mechanical 

 properties of a single medium Avhich exists in the vacuum of space, 

 and is more or less modified by ponderable bodies. We have here 

 a philosophical conception which is not lacking in grandeur, but which 

 makes the task of the mathematicians a peculiarly hard one, and, may- 

 be, extends beyond the range of the human mind. As long as it was 

 only a question of imagining the structure of the medium capable of 

 transmitting light the problem was comparatively easy, and yet it has 

 exercised the sagacity of the most eminent men without our being yet 

 able to affirm that it has been solved. What is it now, when we must 

 turn for everything to a veritable Proteus"? Our successors will not 

 be idle. 



While the alternate currents have taken such a prominent part in the 

 development of theoretical notions, their importance in practice has 

 been just as great. All the methods of producing inductive currents 

 without interruption naturally supply them in the alternating form, 

 because the organs that are brought into operation must revert to tlie 

 same conditions, and that the two halves of each period produce effects 

 in opposite directions. This alternation of the currents makes them 

 for the most part unfit for use. 



At the beginning an effort was made to utilize them by means of cor- 

 rectors, whose object was to drive them upon a neighboring circuit in a 

 constant direction, like a torrent consisting of successive waves. These 

 commutators, however, were so inconvenient that investigations con- 

 tinued for forty years after Faraday's discovery without reaching any 

 practical solution. 



M. Pacinotti had solved the problem in 1864 without imagining that 

 his laboratory apparatus could be applied to industrial purposes. A 



