ELECTRICITY. 509 



ball of the discharger may then be placed on the glass at 

 twelve inches' distance, and the electric fluid will pass as 

 brilliantly over that interval as over the six inches of wa- 

 ter. In either of these experiments if the line of fluid 

 be wider in any particular part, the light of the discharge 

 will be less brilliant in passing that portion. 



5. Electrical heat. 



The electrical spark developes heat as well as light, as 

 may be shown in a great variety of ways. Some experi- 

 ments for this purpose we shall enumerate. 



Inflaming combustibles. Sprinkle upon a light tuft of 

 cotton a quantity of powdered resin, and shake the cot- 

 ton until the resin has penetrated it in every part. Bring 

 then two wires with rounded ends, very near each other, 

 but with the cotton between. Pass now a strong spark 

 from the Leyden jar through the cotton, and it will burst 

 into a flame. 



Pour into a metallic cup attached to the prime conduc- 

 tor, a little elher or alcohol, and then when the conduc- 

 tor is charged, draw a bright spark from the centre of the 

 surface of the liquid. It will be immediately inflamed. 

 Sometimes the experiment is made in another form. In- 

 stead of the cup attached to the conductor, a person 

 standing upon the insulating stool, holds an iron spoon 

 containing the alcohol or ether, and a bystander takes 

 the spark from it by means of a brass ball, or his knuckle, 

 or even a piece of ice. 



Detonating mixtures of gases, especially hydrogen 

 gas and atmospheric air, may be fired by means of 

 electricity. Sometimes they are contained in a strong 

 glass vessel, with two wirag coming on the inside within 

 a short distance of each other. Sometimes a little brass 

 cannon is used, loaded with the explosive gases, and the 

 muzzle stopped with a cork, the said cork being thrown 

 with considerable force among the bystanders by the dis- 

 charge, to the no small amusement of such of them as do 

 not chance to be shot. 



Gunpowder may be fired by the electric spark, under 

 favorable circumstances. In all cases the combustible to 

 be inflamed should be previously warmed. 



VOL. i. NO. xxi. 45 



