Progress of Invention. 75 



consists of two plates of cast iron, placed opposite to each other, 

 and united by two plates of brass. In the ends, which are of some 

 non-magnetic substance, are small circular apertures, that allow 

 an armature to revolve in the axis of the cylindroid. This 

 armature is a cylinder of iron, down the two sides and across the 

 ends of which are deep grooves, within which is wound a helix, 

 formed of copper wire 0.03 of an inch in diameter, and about 160 

 feet in length. When the cylindroid is placed between the poles of 

 a magnet, so that the latter are in good contact with the cast-iron 

 plates, and the armature is made to revolve, it is evident that two 

 opposite electric currents are formed in its helix during each 

 revolution of the armature. All the currents may, by means of a 

 commutator, be made to pass in one direction, and when the rotation 

 is very rapid, the amount of electricity produced by even a 

 single, permanent magnet, is very great ; but every additional 

 magnet placed on the cylindroid causes the addition of an equal 

 effect. If the electric current thus obtained is made to excite one 

 or more electro-magnets, the poles of which are in contact with a 

 cylindroid similar to the first, and the two armatures are made to 

 revolve rapidly, the effect becomes very considerable. And if the 

 second current is transmitted through the helices of other electro- 

 magnets, the poles of which are in contact with a third cylindroid, 

 the third secondary current thus obtained is of great power. 

 With four permanent magnets, each only one pound in weight on 

 the first cylindroid, the armatures in the first two cylindroids being 

 two inches and half in diameter, and that in the third cylindroid 

 ten inches, a current was obtained which, with carbon electrodes, 

 and a parabolic reflector, produced so intense a light on the top of a 

 lofty building at night, that shadows were projected by the flames 

 of street-lamps a quarter of a mile distant. The calorific power of 

 the apparatus sufficed to melt an iron rod a quarter of an inch in 

 diameter, and copper wire 0.125 of an inch in diameter ; and to keep 

 twenty-one feet of iron wire 0.065 of an inch in diameter at a red 

 heat. This instrument seems applicable to lighthouses and 

 numerous other practical purposes ; since it is neither very large 

 nor very costly, and the only expense its working entails is the 

 rotation of the armatures, which should each make about 3000 

 revolutions per minute. Its effects at first sight would appear at 

 variance with the ordinary laws of the conservation of force ; but 

 all difficulty will vanish if we remember that the machine is merely 

 an apparatus for changing rotary motions into electricity. In 

 many cases, the motion required may conveniently be obtained from 

 a steam engine. 



Peroxide of Hydrogen. — This curious compound, which is 

 every day being applied to new uses, and is likely to become a very 

 valuable agent in the hands both of the philosopher and the manu- 

 facturer, may, as Schonbein has discovered, be prepared with great 

 facility, by agitating in a large receiver, into which the air has free 

 access, amalgamated zinc in powder and distilled water. The 

 oxygen of the air combines both with the zinc and water, oxide of 

 zinc and peroxide of hydrogen being formed. The peroxide of 



