18 Professor Tyndall [Jan. 17, 



for alternating currents by which this equal consumption is secured. 

 It will be seen that M. Jablochkoff has abolished regulators altogether, 

 introducing the candle principle in their stead. In my judgment the 

 performance of the Jablochkoff candle on the Thames Embankment 

 and the Holborn Viaduct is highly creditable, notwithstanding a 

 considerable waste of light towards the sky. The Jablochkoff lamps, 

 it may be added, would be more effective in a street, where their 

 light would be scattered abroad by the adjacent houses, than in the 

 positions which they now occuj^y in London. 



It was my custom some years ago, whenever I needed a new and 

 complicated instrument, to sit down beside its proposed constructor, 

 and to talk the matter over with him. The study of the inventor's 

 mind which this habit opened out was always of the highest interest 

 to me. I particularly well remember the impression made upon me 

 on such occasions by the late Mr. Darker, a philosoj)hical instrument 

 maker in Lambeth. This man's life was a struggle, and the reason of 

 it was not far to seek. No matter how commercially lucrative the 

 work upon which he was engaged might be, he would instantly turn 

 aside from it to seize and realize the ideas of a scientific man. He 

 had an inventor's power, and an inventor's delight in its exercise. 

 The late Mr. Becker possessed the same power in a very considerable 

 degree. On the Continent, Froment, Breguet, Sauerwald, and others 

 might be mentioned as eminent instances of ability of this kind. 

 Such minds resemble a liquid on the point of crystallization. Stirred 

 by a hint, crystals of constructive thought immediately shoot through 

 them. That Mr. Edison possesses this intuitive power in no common 

 measure is proved by what he has already accomplished. He has the 

 penetration to seize the relationship of facts and princijDles, and the 

 art to reduce them to novel and concrete combinations. Hence an 

 adverse opinion as to his ability to solve the comi^licated problem on 

 which he is now engaged would be unwarranted. It is purely a case, 

 not for the discovery of new facts and principles, but for the exercise 

 of mechanical ingenuity in turning to a sj)ecial account facts and 

 principles already familiar to the scientific man. 



I will endeavour to illustrate in a simple manner Mr. Edison's 

 alleged mode of electric illumination, taking advantage of what Ohm 

 has taught us regarding the laws of the current, and what Joule has 

 taught us regarding the relation of resistance to the develojiment 

 of light and heat. From one end of a voltaic battery runs a wire 

 dividing at a certain point into two branches which re-unite in a 

 single wire connected with the other end of the battery. From the 

 positive end of tlie battery the current passes first through the single 

 wire to the point of junction, where it divides itself between the 

 branches according to a well-known law. If the branches be equally 

 resistant the current divides itself equally between them. If one 

 branch be less resistant than the other, more than half of the current 

 will choose the freer path. The strict law is that the quantity of 



