Magnetic Characters of Metals^ Sfc. 77 



opened for that purpose, and afterwards closed by a sliding 

 mahogany door. 



When the agitations of the lever have subsided, the slid- 

 ing door is partially opened for the introduction of the poles 

 of a powerful steel horse-shoe magnet, which is made of a 

 long and narrow shape for the purpose. This magnet is 

 placed on a sliding carriage, by means of which it is made 

 to approach the specimen, or recede from it, with great faci- 

 lity, and in the most gentle manner. In consequence of 

 finding decided polarity in some specimens in which no mag- 

 netism was previously known to exist, I have been led to the 

 employment of a powerful bar-magnet, which I find conve- 

 nient in those cases where such polarity is suspected. I 

 have also employed electro-magnets, both straight and of 

 the horse-shoe form ; but having found that these are trou- 

 blesome and inconvenient, I have abandoned the use of them 

 altogether in these inquiries. 



In cases where extreme nicety is required, I have found 

 the following mode exceedingly useful. Besides the sliding 

 door which closes one side of the box, I have an- 

 other sliding piece P, which fits into the same 

 grooves in the side of the box. Through this 

 piece pass two cylindrical rods of soft iron, / /> 

 about 2 inches in length. They are firmly fixed in the 

 wooden slider at their middle parts, and parallel to each 

 other. When this piece is in its place, the iron rods are in 

 the same horizontal plane, having one half within and the 

 other half outside the box, and their inner ends presented to 

 the specimen suspended on the lever. When the remaining 

 portion of that side of the box is closed by the sliding door, 

 the specimen is nicely adjusted to the ends of the iron rods 

 by turning the top piece of the tube, until the most trifling 

 space is perceptible between them. When all is at rest, the 

 poles of the horse-shoe magnet are made to approach the 

 outer ends of the iron rods, bring them into magnetic action, 

 and thus detect the magnetism of the specimen, if any exist 

 in its structure. 



17. By the assistance of this apparatus, to which I give 

 the name Torsion Magnetoscopcy I have examined gold, silver, 



I 



#ri 



