MAGNETO-ELECTRIC INSTRUMENTS. 5*7 



another. The one termed the quantity armature is con- 

 structed of stout iron, and covered with thick insulated 

 wire. The other, the intensity armature, is constructed of 

 slighter iron, and covered with from 1000 to 2000 yards, 

 according to the size of the instrument, of fine insulated 

 wire. 



The quantity armature is adapted for exhibiting the mag- 

 netic spark, inducing magnetism in soft iron, heating plati- 

 num wire, &c. The intensity is best adapted for administering 

 the magnetic shock. A few words will suffice to explain 

 the theory of the magneto-electrical machine, as at present 

 understood ; as often as the bent ends of the armatures or 

 inductors, F, F, F, are brought by the rotation of the wheel 

 opposite the poles of the magnet, they become, by induction, 

 magnetic ; but they cease to be so when they are in the po- 

 sition shown in the cut, viz. at right angles to it. Now, at 

 the moment of the induction as well as of the destruction 

 of the magnetism in an iron bar surrounded by copper wire, 

 opposite currents of electricity are induced in the wire if the 

 circuit be complete ; the points, k, are therefore so arranged 

 that they shall leave the mercury and thus break the circuit 

 in the wire surrounding the armature, F, at the moment 

 that its ends become opposed to the poles of the magnet ; 

 for which purpose they must be placed nearly at right angles 

 to it: the circuit is thus broken at the precise moment that 

 a rush or wave of electricity is determined in the wire, and 

 hence the electrical effects that are obtained. 



Price, $50.00. 



Magneto- Electric Machine. (Fig. 479, next page.) This 

 instrument consists of a compound horse-shoe magnet, com- 

 posed of five bars, and supported on a mahogany base by 

 three brass pillars, being held firmly thereon by a strong 

 screw ; to the base a strong brass pillar is fastened, carrying 

 a brass wheel eight inches in diameter, having a groove in its 

 circumference, and a handle for turning it on its axis. A 

 spindle is supported by a shorter pillar, by passing through 

 and working against a collar, and supported at the end by a 

 screw in the longer pillar, the point of which enters the cen- 

 tre of the spindle. To the end of the spindle, projecting 

 through the shorter pillar, is fixed an armature, consisting 

 of a bar of soft iron, bent at right angles, and surmounted 

 with coils of fine insulated copper wire, each coil wound in 



