ELECTRIC LIGHTING. 77 



rier, which should present sufficient resistance to its passage 

 to become bodily incandescent without disruption. 



This was the essence of the invention specified in King's 

 Patent as " a communication from abroad," which claims the 

 use of continuous metallic and carbon conductors, intensely 

 heated by the passage of a current of electricity, for the 

 purposes of illumination. 



The metal selected was platinum, which, as the specifi- 

 cation states, "though not so infusible as iridium, has but 

 little affinity for oxygen, and offers a great resistance to the 

 passage of the current." The form of thin sheets known 

 by the name of leaf-platinum is described as preferable. 

 These to be rolled between sheets of copper in order to secure 

 uniformity, and to be carefully cut in strips of equal width, 

 and with a clean edge, in order that one part may not be 

 fused before the other parts have obtained a sufficiently high 

 temperature to produce a brilliant light. This strip to be 

 suspended between forceps. 



I need not describe the arrangement for regulating the 

 distance between the forceps, for directing the current, etc., 

 as we soon learned that this part of the invention was of no 

 practical value, on account of the narrow margin between 

 efficient incandescence and the fusion of the platinum. 

 The experiments with the large battery that I made con- 

 sisting of 100 Dauiell cells, with two square feet of working 

 surface of each element in each cell, and the copper-plates 

 about three-quarters of an inch distant from the zinc 

 satisfied all concerned that neither platinum nor any 

 available alloy of platinum and iridium could be relied 

 upon ; especially when the grand idea of subdividing the 

 light by interposing several platinum strips in the same 

 circuit, and working with a' proportionally high power, was 

 carried out. 



This drove Mr. Starr to rely upon the second part of the 

 specification, viz., that of using a small stick of carbon made 

 incandescent in a Torricellian vacuum. He commenced 

 with plumbago, and, after trying many other forms of car- 

 bon, found that which lines gas-retorts that have been long 

 in use to be the best. 



The carbon stick of square section, about one tenth of 



