ELECTRO-MAGNETIC INSTRUMENTS. 



Fi. 463. Fig. 46 1. 



41 



such as silver and platinum, soldered together and arranged 

 in a rectangle, with a ring in the lower part for the intro- 

 duction of a support. When the pole of a magnet is placed 

 on one side of the frame and a spirit lamp on the other, the 

 wire frame rotates by thermo-magnetic action. 



Price, $1,75 : with stand, $2,25. 



Fig. 465. 



Thermo- Electric Revolving Rect- 

 angles. (Fig. 465.) This instru- 

 ment consists of a U magnet, mount- 

 ed on a brass stand, having a well 

 finished centre in each of the poles ; 

 two rectangular frames composed of 

 silver and platina, or silver and 

 German silver, are delicately poised 

 on the centres, and a spirit lump 

 that can be adjusted to different 

 heights, fixed between the arms of 

 the magnet, the flame of which 

 causes the circulation of thermo- 

 electric currents in the wires as 

 evinced by their rotation round the 

 poles of the magnet. 



Price, $6.00. 



Flat Ribbon Coils. (Fig. 466, 

 next page.) These consist of sheet 

 copper, cut in strips about one inch 

 wide, and soldered together to the length of 190 feet or 

 more, and wound together in the form of a close spiral, 

 each layer carefully insulated by strips of cotton. 



Professor Henrv, of Princeton, to whom we are indebted 



