28 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



in the centres of the ends of the magnet, two conical pointed 

 wires are inserted, which are affixed in the middle of two 

 hemispherical cups, united to cylinders, the rims of which 

 are formed into points, which are dipped into the mercury, 

 contained in the circular troughs. Upon the top of each 

 hemisphere is placed a small cup, to contain mercury. Other 

 cups for holding mercury, are supported on the external 

 ends of bent wires, which pass through the sides of the 

 circular troughs, into the mercury contained therein. When 

 a stream of voltaic electricity is passed through this appa- 

 ratus, by means of connecting wires, placed in the mercury, 

 contained in the upper and lower cup, the cylinders com- 

 mence revolving in opposite directions, that cylinder on the 

 north pole, and down which the current is descending, 

 moving of course from left to right ; but if the two upper 

 cups be united by a wire, and the lower cups connected 

 with the positive and negative extremities of the voltaic 

 battery, the same stream will traverse both sides of the ap- 

 paratus, passing upwards in one cylinder, and downwards 

 in the other ; and the rotations will now, from the contrary 

 influences of the two poles, be in the same direction in both 

 cylinders. Price, $8.00. 



Page 1 s Revolving Armature. (Fig. 448, next page.) This 

 consists of a U formed electro-magnet, wound with stout 

 insulated copper wire, supported on a round mahogany base, 

 in a vertical position, and having a brass plate soldered 

 around the poles of the magnet, and supporting a brass pillar 

 and arm at one end. Over the poles of the electro-magnet 

 there revolves a soft iron armature, having a spindle sup- 

 ported in a centre below, and a screw in the arm above ; on 

 the spindle near the armature there is a break-piece formed 

 of silver, by filing the opposite sides away, and against 

 which a silver spring is fixed' so as to touch the break-piece 

 twice in each revolution, and having a wire connected with 

 the cup, having a binding screw on the base, the termina- 

 tions of the wires of the electro-magnet being with the other 

 cup on the base, and with the iron of the magnet. On con- 

 necting the battery current with the cups on the base, the 

 armature will revolve with great rapidity. Price, $4.00. 



Revolving Wheel and Armatures. (Fig. 449, next page.) 

 This consists of a wheel, having four soft iron armatures 



