336 



ELEOTEIO LIGHT, EDISON'S. 



portant applications of electricity with duplex, 

 quadruplex, and quite recently sextuplex te- 

 legraphy; with the electric pen; with some of 

 the best forms of the telephone and its various 

 modifications, as the microphone, the micro- 

 tasimeter, the megaphone, the aerophone, the 

 phonometer; with the phonograph (see biog- 

 raphy of THOMAS ALVA EDISON, in "Annual 

 Cyclopaedia " for 1878) when it was reported 

 that this indefatigable experimenter and ver- 

 satile inventor had turned his attention to the 

 problem of electric illumination, the public 

 expected that his fertile and practical mind 

 would succeed if it were possible in overcom- 

 ing the minor but stubborn difficulties which 

 yet stood in the way of electrical illumination. 

 The confidence which was felt in his ability is 

 shown by the fact that during the months in 

 which he was engaged in studying this subject, 

 newspaper rumors of the success or non-success 

 of his laboratory studies made the prices of gas- 

 stock rise or fall on the Paris and London Ex- 

 changes. He commenced his experiments in 

 September, 1878, and, after fifteen months of 

 research, in the latter part of December, 1879, 

 he published the record of his investigations to 

 the world, and gave a public trial of the elabo- 

 rated result. 



Divining that the practical electric light of 

 moderate illuminating power could not be pro- 

 duced by the voltaic arc, to which recent ex- 

 periments have been chieiiy confined, and with 

 which Jablochkoff, Serrin, Werdermann, and 

 others have obtained remarkable results, but by 

 the incandescence of some resistant material, 

 he confined his attention to the substances ol 

 low conducting powers from which the incan- 

 descent light can be obtained. These are plat- 

 inum, iridium, and like metals and alloys, 

 which only fuse at an exceedingly high tem- 

 perature, and the forms of carbon which pos- 

 sess a high degree of purity and homogeneity. 

 His earlier experiments were expended upon 

 metallic material. Considering that the incan- 

 descence of the metal is the greater, the stronger 

 the electrical current to which it is subjected, 

 he directed his thoughts first to the invention 

 of a regulating apparatus which would auto- 

 matically break off the current when the tem- 

 perature of the metal approaches the point of 

 fusion. Constructing a lamp with a double 

 platinum spiral as the incandescent conductor, 

 he inserted within the spiral a platinum rod 

 connected with a lever, one end of which is 

 connected with the wire which conducts the 

 current to the platinum spiral, and the other 

 end of which is a circuit-closer, which being 

 lowered closes the circuit with the wire which 

 conducts off the current, causing it to pass 

 through the lever and deflecting it from the 

 incandescent platinum conductor. The expan- 

 sion of the platinum rod by the heat presses 

 down the end of this lever, forming the neces- 

 sary continuous metallic counection, and clos- 

 ing the circuit below, but only momentarily, 

 since the lowering of the temperature of the 



spiial instantly causes the rod to contract, 

 breaking the new circuit until the heat of the 

 spiral again rises to the dangerous point. This 

 device was, however, found to be untrustwor- 

 thy after a certain period of use, the pressure 

 of the rod upon the lever after a while bending 

 it out of shape. Among the other circuit- 

 closing regulators which he devised was one 

 by which the heated air pressed a diaphragm 

 outward, closing and breaking the circuit so 

 rapidly that no variation in the intensity of the 

 light was observable. Another was a device 

 by which the expansion of the luminous con- 

 ductor itself was made to draw a rod upward, 

 which actuated a circuit-closer through an ar- 

 rangement of levers. Edison developed in the 

 earlier stages of his investigations a novel kind 

 of lamp, from which he obtained a very bril- 

 liant light by the incandescence of a piece of 

 zircon to which the heat-rays of the incandes- 

 cent platinum spiral were transmitted by reflec- 

 tion. The spiral of platinum and iridium was 

 placed in the focus of an elliptic reflector of 

 copper coated with gold, and the heat-rays 

 were focalized upon a thin piece of zircon, 

 which attained a degree of luminosity greatly 

 exceeding that of the incandescent platinum. 



Edison's experiments were necessarily direct- 

 ed mainly to the material to be rendered incan- 

 descent, and the form in which it will afford 

 the best results. The brilliancy of the light 

 depends upon the resistance which the incan- 

 descent conductor offers to the passage of the 

 electric current. Expecting the best results 

 from platinum, he found that the light was in- 

 tensified by incorporating fine particles of this 

 conducting agent in a non-conducting, incom- 

 bustible, and non-fusible material, which was 

 itself rendered luminous by the heat. By imbed- 

 ding finely divided platinum in a non-conduct- 

 ing substance, he obtained a light from currents 

 too weak to render the spiral luminous. A 

 large spiral of platinum whose coils were coat- 

 ed and separated by magnesia produced a good 

 light ; it was with this form of lamp that he 

 employed the regulator in which a metallic cup 

 at the top of the coil pulled a rod upward, ac- 

 tuating a circuit- closing apparatus. Among 

 the other materials upon which he experiment- 

 ed were the oxides of different metals. He 

 obtained a fine light from iridosmine, a natural 

 alloy of osmium and iridium, which he inclosed 

 in a powdered state in a tube of zircon. He 

 tried also a combination of platinum and car- 

 bon, the latter becoming highly incandescent 

 as the current passed to it from the platinum 

 rod, encountering a greater resistance. 



Still considering platinum the most promis- 

 ing material, he was startled after a couple of 

 months of experimentation by the discovery 

 that the platinum degenerated, and that its in- 

 candescence was seriously affected through the 

 action of the atmosphere. Plates and wires of 

 platinum, and also of iridium and other metallic 

 conductors whose point of fusion is at a very 

 high temperature, he found, when heated while 



