464 Mr. Warren Be La Hue [Jan. 21, 



high potential, and at the time of his death there were 3000 

 Leclanche cells in action at his laboratory; on January 26th, 1875, 

 I measured the length of the spark between points and found it to be 



• 025 inch ; 3000 of our cells produced a spark of more than twice 

 this length, namely • 0564 inch, on account of its better insulation. 



I propose, in order to show the power we have at command, in 

 the first instance to accumulate, by means of a condenser, the 

 electricity from 3240 cells, and to send its charge through a platinum 

 wire -^Q of an inch thick. In charging the condenser I will pass the 

 current through a voltameter, in order that you may judge of the 

 very small chemical force concerned in the production of the enor- 

 mous mechanical effect of the electric discharge. I may as well at 

 once tell you that the current necessary to charge the condenser I am 

 employing would decompose merely ^^qVo ^^ ^ grain of water. I will 

 first of all pass the current from twenty cells through the voltameter ; 

 you will see that there is a rapid evolution of mixed gases (oxygen 

 and hydrogen) into which the water is resolved. The evolution of 

 gas, you will at once perceive, is very much slower when the current 

 is charging the condenser; also it is more rapid at fii'st and then 

 gradually lessens, and would entirely cease if there were no leakage 

 of the charge. 



When I send the charge of the condenser, which has the enormous 

 capacity of 42 * 8 microfarads * (or equal to 6485 Leyden jars, like that 



1 have before me, which has coatings of 442 square inches), through 

 2i inches of gold wire -^^ inch diam. strained on a glass plate, it will be 

 violently deflagrated with a loud report, and the metal will be scattered 

 into dust, which the microscope shows to be composed of minute metallic 

 globules, and not an oxide resulting from combustion. Faraday proved 

 that the quantity of electricity necessary to produce a powerful flash 

 of lightning would result from the decomposition of a single grain of 

 water. This can be realised when it is remembered that it would be 

 5000 times as great as the charge of the 42-8 m.f. condenser just 

 shown you. If we place the glass plate on which the wire was 

 strained before the microscope, then it will be perceived that the 

 distribution of particles of gold is not uniform along the space which 

 the wire occupied, but on the contrary, they present a stratified 

 appearance, indicating a series of pulsations during the apparently 

 instantaneous discharge. I hope to show you shortly that the most 

 steady discharge through a vacuum tube is in reality intermittent. 



As I shall for this purpose cause the current passing through the 

 tube to pass at the same time through an induction coil, so as to 

 induce a secondary current, I will render evident to you, in a striking 

 manner, that when electricity is caused to pass through a wire, it 

 induces another or secondary current in an adjacent wire. I have 



* A condenser, which holds the charge of a current produced by 1 volt 

 working for 1 second through a resistance of 1 ohm to a potential of 1 volt, has 

 the capacity of 1 farad. The farad is too large a quantity for practical purposes, 

 therefore the millionth part of it, or the microfarad, is employed as the unit of 

 capacity. 



