MAGNETO-ELECTRIC MACHINE. 181 



The general principle of this instrument will be seen il- 

 lustrated in the engraving. It is called a magneto-electric 

 machine, as it is one for developing electricity by means of 

 magnetism. Apparatus which operates on the converse 

 principle that is, of developing magnetism from electrici- 

 ty, is called electro-magnetic. 



The bobbins that is, the bars of soft iron wound with 

 conducting wires are in the centre, in a great measure 

 out of view, being arranged around the axis of the ma- 

 chine. This axis may be rapidly revolved by means of 

 the band and pulleys seen above, which bring in mechan- 

 ical force provided either by steam or horse power from 

 the adjoining room. The ends of the bars within the bob- 

 bins pass, as they revolve, across the face of the poles of 

 the powerful horseshoe magnets which are seen arranged 

 in tiers on the outside. There are eight ranges of these 

 magnets, with seven in a range. The magnetic condition 

 of the iron bars is changed, of course, with amazing rapid- 

 ity when the axis is made to revolve at considerable speed. 

 At each change an impulse of electrical force is imparted 

 to the wires around the bobbins. These impulses are com- 

 bined by means of the proper connections, and thus become 

 practically a continued stream, which passes to and is re- 

 turned from the carbon points in the instrument on the 

 left. The small square box above the pedestal contains 

 the apparatus for regulating the distance of the carbon 

 points from each other, this being necessary to secure 

 steadiness and uniformity in the light. 



The whole process, as exemplified in this apparatus, fur- 

 nishes a very remarkable and very comprehensive illustra- 

 tion of a principle which is one of the greatest, if not the 

 very greatest scientific discovery of modern times, namely, 

 that of the correlation of force. The principle is, that all 

 the great forces of nature mechanical motion, electricity, 



