in the Metallic Cross, 49 



mony and bismuth cross soldered, and even the soldered bismuth 

 bars are superior to the original form. 



The change in the direction of the primary current in the 

 results from the antimony and bismuth cross, where AC repre- 

 sented the bismuth bar, show how much the induced current is 

 influenced by the thermo-electrical current developed at E ; for 

 with the primary current passing in the direction DEA, the 

 induced effect at E is opposed to a thermo-electrical current 

 generated by heat there ; with the primary moving in the direc- 

 tion AED, the induced and the thermo-electrical current both 

 generated at E are in the same direction. The effect of the 

 thermo-electrical current opposing or exalting the induced cur- 

 rent, is to change the deflection of the galvanometer 5°; a fact 

 which is strong evidence of how little in a bismuth and antimony 

 cross thermo-electricity has to do with the results. 



Although it is easy to construct a cross of copper which will 

 give no permanent current in the second pair of arms BEC, I 

 fear that this would not be practicable with bismuth, it is so 

 exceedingly liable to variations in density in different parts of 

 the castings. 



In conducting these experiments, the immediate effect of the 

 primary current in generating the induced one shows that un- 

 equal heating of the bars is not requisite ; for this requires time, 

 while the induced current is at its highest the instant the pri- 

 mary circuit is completed. 



These feeble induced currents are clearly due to a slight in- 

 terruption or resistance the main current meets with while pass- 

 ing from one arm of the cross to the other. The three experi- 

 ments with the copper cross show this ; but in a subsequent set 

 of three with a zinc cross, the evidence was still more marked. 



Deflection. 



Cross of rolled zinc tied with cord at centre, and! ~ 2 



surfaces slightly oxidized J 



Cross of rolled zinc tin soldered, superficies sol-1 OF - 



dered '002 of a superficial inch .... J 



Cross of rolled zinc tin soldered, superficies sol- 1 no deflec- 



dered *073 of a superficial inch . . . . J tion. 



A friend has suggested that these currents in the other arms 

 of the cross may be derived from the main current without in- 

 duction, or, in fact, are a portion of it. To try this, I constructed 

 a bismuth cross of long and short arms, where the main current 

 had to traverse two inches of the bad conducting metal, and the 

 other current had fourteen inches of the same to pass. In such 

 an arrangement the main or battery current would experience a 



Phil. Mag. S. 4. Vol. 6. No. 36. July 1853. E 



