178 Ml". J. Goodman's Researches into the Identity of 



free from magnetic polarity, I proceeded to draw the file 

 several times over the surface of the wire, when, by holding 

 them on each side the north pole of a suspended magnetic 

 needle, it was found that the wire attracted, and the file re- 

 jielled, this pole with considerable force. 



Exp. A new file attracted both poles of a magnetic needle, 

 or was unmagnetic. A piece of iron wire sMghtly repelled t\\e 

 pole. After rubbing the wire along its surface, and holding 

 the wire on one side of the north pole and the file on the other, 

 tiie needle was attracted bij the loire and repelled by ihejilc. 



Exp. A new file attracted the north pole of a magnetic 

 needle 10°; a piece of iron wire repelled the same. After filing 

 the same and placing this pole of the needle between them, 

 the file repelled and the wire attracted the needle. This ex- 

 periment was repeated with the same result. 



A thick file and a thick piece of soft iron did not produce 

 any change, the process not being sufficiently powerful to in- 

 duce magnetic polarity in any considerable mass of metal*. 



Exp. Another file was neutral, rather attractive. The re- 

 pulsive end of a piece of magnetic iron wire was employed. 

 After filing briskly around the surface of its extremity, \.\\Qjile 

 repelled and the 'isire attracted the north pole. 



Exp. Took the opposite extremities of the file and wire; 

 the wire repelled, the file attracted ; but on rubbing them 

 together, an instant change took })lace; the j^7^ repelled^ and 

 the wire attracted the needle. 



Repeated with the same results. These operations were 

 performed when the metals pointed southward. It was dis- 

 covered, however, that an opposite result took place when the 

 filing was performed towards the north. The file then at- 

 tracted, and the wire repelled the north pole; but the evinced 

 trifling difference of affinity between iron and steel, as shown 

 in (15.), may tend to produce this uncertainty, which subjects 

 them to tlie government of the earth's polarity. 



Is the current induced by mechanical operations simply 

 thermo-electric, or not? 



Exp. VI, Immersed the lower half of the bismuth cylinder 

 in water at 55°, By turning it with a steel tool about one 

 minute (the water revolving around the cylinder the whole 

 period), a current was constantly maintained, at length from 

 35° to 40°, fine turnings being produced. 



Tiie water, 9 oz. and 2 drs., in which the bismuth disc v.as 

 immersed, and which would derive the principal part of the 



* The finer the materials employed, the more highly developed were 

 the magnetic effects j and on this account iron wire was used, 



