Lesson V. 





141 



so that the accumulated opposite electn- 

 citirs of the two surfaces pass from one 

 to the other. To use this rod apply 

 one ball to one surface, and then apply 

 the other, when a vivid spark aad ex- 



vil he produced. 



53 T. What is the Loyden j.ir? 

 P. A glass jar or bottle coated with 

 tin-foil ins'de and out- 

 side, as high as (a Fig. 

 19) in the one on the 

 table, and therefore leav- 

 ing a rim of naked 

 glass above the tin-foil. 

 The mouth of it is 

 fitted with a woo : 

 which bus a brass rod pass- 

 ing thr.wch its centre, to 

 the upper end of which 

 a brass hall is attached, 

 and a brass chain to the 

 i', lower part. 

 /'. What is the principle of the 

 jar? 



A modification of Franklin's j late. 

 T. Are not several of these jars 

 3>nietimes u: 



l\\ - done in order to obtain 



s'rong charge ; and in this ease we 

 are obliged to employ larger jar?, and then 

 the brass ball of t-.ich jar i* connected 

 with its fellow, and all the external 

 coatings of the jars are in connection 

 with each other, ax well as the inn.r 

 coatings. \N h n this combination 

 1-l.it-e the apparatus is called an electric 

 battery. 



GENERAL QUESTIONS ON LESSON IV. 



1. What is the effect of the distance 

 being increased between bodies? 



2. Is there any objection to ur using 

 ansuhr and sharp edges to conducting 

 bodies? 



3. Explain the distribution of electricity 

 on the surfaces of conducting bodies. 



4. How does a Franklin's plate act? 



.">. How can we discharge a Franklin's 

 plate? 



6. Explain what is meant by a Leyden 

 jar and au tlectric battery. 



LESSON V. 



WE know that when electricity has accumulated in a body and is discharged, that a 

 light is produced, but that the body will not afford the least appearance of light as long 

 at a state of electric equilibrium subsists, and the two electricities are und-sturbed. The 

 distance at which a spark can be drawn from an electric body depends upon the 

 conductability of the substance, the power of the electric discharge, and the sue of 

 the corfaee. A powerful charge is required to make round bodies emit sparks 

 spontaneously, but angular or pointed bodies will emit sparks with a very weak 

 charge. Sparks are multipli -rupttng the conductor by which the t-l.-ctricity 



to the earth. Thi may easily be proved by ex p. rim. -nt. [K\; 



Tike a plate of glass of the same shape as /'<</. 20, and fasten a brass ball to 

 the top of it, and connect this brass ball with another at the botton 

 means of rbomboidal or dimond-haped plates of tin-foil j>..sted on the 

 glass, hut so arranged that they do not touch each <.th. r Connect the 

 lower ball with the outer coating < : . jar, and the upper ball with 



tli- knot) of i will then M-e sparks IK twen each pie- 



[Does to, and the effect produced in the dark is beautiful]. [Kxperimeat 

 10.] I have here a glass plat* (Fiy. 20) wli 

 jty. o. colours, red, blur, and yellow, and covered with pieces of tin foil, the sane 



