Lesson VIII. 



ELECTRICITY. 



147 



dered togetlu--, whose susceptibility to heat j 

 as heat is applied ' 

 to the two places of junction, an electric 



-oduced and maintained as j 

 the difference of temperature con- 

 -::mth and copper answer very 

 <>r this purpose. 



/". N it necessary to employ me- 

 tals? 



/'.No; it is found that if hot water 



and cold water are mixed together, that 



Li produced, and that the hot 



Peonies negative, and the cold 



;<>*itive ; but the reverse takes place 



with acids ; for if a hot acid is mixed with 



a cold one. the former becomes positive, 



and the latter negative. 



aid that bismuth and 

 answered very well ; can you i;i- 

 me of any other metals that ab- 

 used? 



< ertainly. This table will exhibit 

 the order of the principal metals in 



combinations, and the 

 farthest asunder any two metals are placed 

 in this Table, the more powerful is the 



hem. 



Kach metal causes a positive current to 

 la-s upon any metal above it, and a nega- 

 tive- upon any metal below it; therefore, 

 if bismuth and antimony were solden-d 

 together, a negative current would pass 

 from the antimony to the bismuth, and a 

 positive one from the bismuth to the anti- 

 mony; negative electricity radiates from 

 the junction through the bismuth, and 

 positive electricity through the antimony. 



'J'2. T. Is it possible to form a com- 

 pound thermo-electric circuit ? 



I*.- Yes ; by joining several bars of 

 metals together; but then the heat re- 

 quires to be applied to each joining : ther- 

 mo-electric piles may be constructed as 

 well as voltaic piles. 



RAL QUESTIONS ON LESSON VII. 

 1. How can we form temporary 



J. How do you know the north from 

 the south pole of a magnet ? 



3. Is it possible to cause motion by the 

 ilvanic current? 



4. Upon what principle is them* 

 'city produced? 



5. Describe the method of obtaining au 

 electric current by heat, and nai 



erally empfc 



-SON VIII. 



FOE many obvious reasons we have placed magnetism, the subject of the present 

 lesson, last on our list 



We have already seen :ro|1 may ^ imparted tem . 



and permanently to steel ; but certain iron ores which have this 



rty are found in the earth, and are termed natural magneto. 



are generally made ii .;, ^ ^4 horse-shoes. 



QUI 



amag- 

 i'gs, what 

 the co 



will be r. 



U>cause 

 s or jtoftt than in 



ippose that I brke the msg- 

 -I'.-d the 



two pieces into the iron liliiiL's, what 

 would bet! 



v the same, because each 

 ome a perfect magnet, 

 having its neutral line and two poles. 

 95. 7 :! a magnet by a 



rd (as in Fiy, 26^ what will be 

 the effect? or bringing one pol 

 magnet n, ar c-iih.-r of the two poles of the 

 t is suspended? 



