Homogeneous Bodies; "with illustrative Experimerits. 7 



26. Experiments with the rectangle A. — The arrows in fig. 4. 

 will, in general, indicate the direction of the electric currents 

 in this piece of bismuth. There are, howevei', circumstances 

 connected with the experiments which require some further 

 explanation. — I shall endeavour to point out these particulars 

 with some degree of minuteness, commencing with those which 

 were observed when the point of heat was on the side a b ; 

 and proceed successively with the other sides according to the 

 regular order of the letters. 



Side ab. Current. 



Tclose to a none ") 



T» ■ «. r- one inch from a ... very feeble ... I r ^ i 



Point oi I . n 7 -' f 1 > irom a to b. 



, ^ centre oi ab more powertul [ 



I one inch from b ... very powerful J 



Inclose to i very powerful from 6 to «. 



Neutral point '5 inch from b. 



Side be. 



T% • ^ c r close to Z* powerful ") r. , ^ 



romt or I ^ r. T ^ c ^ t irom b to c. 



, < centre oioc powerful j 



Lclose to c powerful from c to b. 



Neutral point '25 from c. 



Side c d. 



fclose to c powerful 1 r j. 



p . f. I one mch irom c ... leeble j 



, ^ <^ centre ofct? powerful 1 ^ ^ , 



neat > ■ \ c i c ^i■ ii'om c to a. 



I one mch irom a ... more powertul J 



Inclose to rf powerful from £? to c. 



Neutral points '75 inch from d, and 1*5 inch from c. The 

 latter was the gate or point at which the metal entered the 

 mould. 



Side d a. — To whatever part of this side of the rectangle 

 heat was applied, the electric current flowed from a to d; but 

 the energies were more powerful when the point of heat was 

 close to c/, than when in any other part of the side d a. 



27. It will be observed that in this rectangle there are only 

 two of the angles, a and 6, which are neutral points. The 

 other angles, c and d, when heated produce very powerful 

 electric currents; indeed, much more so than when the point 

 of heat is in any other part of the metallic frame. When those 

 two angles are heated at the same time, their energies being 

 excited in the same direction, conspire to ))roduce effect on the 

 needle, which becomes much more deflected than when one 

 angle only is heated. Precisely the same thing happens when 

 any other two or more points are simultaneously heated, the 



energies 



