108 NeiD Electro- Magnetic and Magneto- Electric 



showing the spark of a magneto-electric machine, that is fur- 

 nished with the contrivance, called by Dr. Page a ujiitrep, for 

 causing the current induced by the magnet lo flow in a constant 

 direction. By making the proper connections, the magneto-elec- 

 tric current may be made to circulate through the inner helix in 

 the same way as the voltaic current, producing sparks in the glass 

 cups, and, if the handles connected with the outer helix be grasp- 

 ed, slight shocks. In addition to the experiments I have enume- 

 rated, the double helix and electrotome may be used for most of 

 the purposes of a common simple helix. 



Separable Helices and Revolving Armature. — This instru- 

 ment, represented by figure 2, is similar in many respects to the 

 preceding, and will require but little description. The two heli- 

 ces are composed of wires of about the same length and size, as 

 those of the double helix and electrotome, but entirely discon- 

 nected with each other, so that the outer may be removed from 

 the inner one. The latter is firmly secured in a vertical position 

 to a base-board, underneath which one set of similar ends of its 

 wires is soldered to the cup A, and the other set to the cup B. 

 R R is a steel rasp, confined in close contact with the cup B. 

 P P is a modification of Page's revolving armature, described in 

 Vol. XXXV, p. 262, of this Journal. The extremities of the wire 

 wound round the two branches of the electro-magnet, are respec- 

 tively coimected underneath ihe base-board with the cups Band C. 

 The voltaic current may be transmitted in sequence through this 

 instrument and the inner helix, by connecting the cups, A and G, 

 with a battery. It is here used to break the battery current, 

 which it does twice during each revolution of the armature. 

 The battery current may be broken, without including the revol- 

 ving armature in the voltaic circuit, by connecting one of the 

 battery wires with the cup A, and drawing the end of the other 

 over the steel rasp, in which case brilliant scintillations will be 

 produced, S and S are cups fastened to brass caps, longitudin- 

 ally divided, which enclose the ends of the outer helix, and to 

 which the ends of the wire composing it are soldered. In the 

 figure there is seen, projecting from the upper end of the inner 

 helix, a brass tube filled with iron wires, which may be with- 

 drawn. This instrument is peculiarly suited to the lecture-room 

 on account of its simplicity, and the facility with which the 

 powers and uses of its several parts may be separately exhibited. 



