34 Mr. JosejiJi W. Sican [March 10, 



the illninination of such large enclosed spaces as railway stations; 

 but it is totally unsuited for domestic lishtincr, and for nine-tenths of 

 the other purposes for which artificial light is required. If electricity 

 is to compete successfully with gas in the general field of artificial 

 lighting, it is necessary to find some other means of obtaining light 

 through its agency than that with which we have hitherto been 

 familiar. Oui* hope centres in the method — I will not say. the new 

 method — but the method -which until within the last few years has 

 not been applied with entire success, but which, within a recent 

 period, has been rendered perfectly practicable — I mean the method 

 of producing light hy electrical incandescence. 



The fate of electricity as an agent for the production of artificial 

 light in substitution for gas, depends greatly on the success or non- 

 success of this method ; for it is the only one yet discovered which 

 adapts itself with anything like completeness to all the pm'poses for 

 which artificial lighting is required. 



If we are able to produce light economically through the mediimi 

 of electrical incandescence, in small quantities, or in large quantities, 

 as it may be required, and at a cost not exceediug the cost of the same 

 amount of gas light, then there can be little doubt — there can, I think, 

 be no doubt — that in such a form, electric light has a great future 

 before it. I propose, therefore, to explain the principle of this 

 method of lighting hy incandescence^ to show how it can he applied, and 

 to discuss the question of its cost. 



When an electrical current traverses a conducting wire, a certain 

 amount of resistance is opposed to the passage of the current. One 

 of the eftects of this conflict of forces is the development of heat. The 

 amount of heat so developed depends on the nature of the wire — on 

 its length and thickness, and on the strength of the current which 

 it carries. If the wire be thin and the current stronsr, the heat 

 developed in it may be so great as to raise it to a white heat. 



The experiment I have just shown, illustrates the principle of 

 Electric Lighting by Incandescence, which is briefly this — that a state 

 of white heat may he produced in a continuous solid conductor hy passing 

 a su^ciently strong electrical current through it. 



A principle, the importance of which cannot well be overestimated, 

 underlies this method of producing light electrically — namely, the 

 principle of divisibility. By means of electric incandescence it is 

 possible to produce exceedingly small centres of light, even so small 

 as the light of a single candle ; and with no greater expenditure of 

 power, in proportion to the light produced, than is involved in the 

 maintenance of light-centres 10 or 100 times greater. Given a cer- 

 tain kind of wire, for example a platinum wii-e, the 100th of an inch 

 in diameter, a certain quantity of current would make this wire white- 

 hot whatever its length. If in one case the wire were one inch long 

 and in another case ten inches long, the same current passing through 

 these two pieces of similar wire, would heat both to precisely the 

 same temperature. But in order to force the same current thi'ough 



