THE ELECTRIC LIGHT. 569 



with the gas-pipes, the circuit is incomplete and no current will flow ; 

 but if any part of the main, however distant from the battery, be con- 

 nected with the adjacent gas-pipes, the circuit will be completed and 

 the current will flow. Supposing our battery to be at Charing Cross, 

 and our rod of copper to be tapped opposite Somerset House, a branch 

 wire can be carried from the rod into the building, the current passing 

 through which may be subdivided into any number of subordinate 

 branches which reunite afterward and return through the gas-pipes to 

 the battery. The branch currents may be employed to raise to vivid 

 incandescence a refractory metal like iridium or one of its alloys. 

 Instead of being tapped at one point, our main may be tapped at one 

 hundred points. The current will divide in strict accordance wuth law, 

 its power to produce light being solely limited by its strength. The 

 process of division closely resembles the circulation of the blood ; the 

 electric main carrying the outgoing current Kepresenting a great artery, 

 the gas-pipes carrying the return current representing a great vein, 

 while the intermediate branches represent the various vessels by which 

 the blood is distributed through the system. This, if I understand 

 aright, is Mr. Edison's proposed mode of illumination. The electric force 

 is at hand. Metals sufficiently refractory to bear being raised to vivid 

 incandescence are also within reach. The principles which regulate the 

 division of the current and the development of its light and heat are 

 perfectly well known. There is no room for a " discovery," in the sci- 

 entiBc sense of the term, but there is ample room for the exercise of 

 that mechanical ingenuity which has given us the sewing-machine and 

 so many other useful inventions, and which engages a greater number 

 of minds in the United States than in any other nation in the world. 

 Knowing something of the intricacj'^ of the practical problem, I should 

 certainly prefer seeing it in Mr. Edison's hands than in mine.* 



It is sometimes stated as a recommendation to the electric light, that 

 it is light without heat ; but to disprove this it is only necessary to 

 point to the experiments of Davy, which show that the heat of the vol- 

 taic arc transcends that of any other terrestrial source. The emission 

 from the carbon points is capable of accurate analysis. To simplify 

 the subject, we will take the case of a platinum wire at first slightly 

 warmed by the current, and then, through the gradual augmentation 

 of the latter, raised to a white heat. When first warmed, the wire 

 sends forth rays which have no power on the optic nerve. They are 

 what we call invisible rays; and not untU the temperature of the wire 

 has reached nearly 1,000° Fahr. does it begin to glow with a faint, red 

 light. The rays which it emits prior to redness are all iisvisible rays, 

 which can warm the hand but can not excite vision. When the tem- 

 perature of the wire is raised to whiteness these dark rays not only 

 persist, but they are enormously augmented in intensity. They consti- 



* More than thirty years ago the radiation from incandescent platinum was admirably 

 investigated by Dr. Draper, of New York. 

 VOL. XIV. — 37 



