DOVE ON THE ELECTRICITY OF INDUCTIO.V. 163 



be directly admitted into the domain of common experimental 

 demonstrations. 



68. The primary current was produced by a Saxton's ma- 

 chine, represented at fig. 7? and constructed by M. Oertling, in 

 which the interruption is effected by means of brass springs, 

 which slide upon two iron cylinders inlaid with pieces of wood. 

 The first of these cylinders, Wj, is fixed in an insulated manner 

 upon the axis A B of the keeper, and holds the end of the wire n 

 composing the coil of the keeper ; the second, Wg, is directly con- 

 nected with this axis, and hence in conducting connexion with 

 the other end of the coil p. The inlaid portions, composed of 

 wood, of the cylinder w^, Wc^ and w^, occupy half the circumference 

 of this cyhnder ; that which is seen at a in the middle of the 

 cylinder Wg however occupies only one-sixth of its circumference, 

 and diametrically opposite it, is another corresponding to it, for 

 the production of alternating currents of equal intensity. One 

 of the springs 1) or 5) slides continuously upon the first cylin- 

 der, as does 9) upon the second, the third 3) either in the same 

 manner uninterruptedly, or it passes once* at an azimuth of 

 90° {i. e. in a rectangular position of the keeper, perpendicular 

 to the line connecting the poles of the magnet), or twice at an 

 azimuth of 90° and 270° over the insulating surface of inlaid 

 wood. In the first case (which only occurs with galvanometric 

 tests and chemical decompositions), the wire of the coil of the 

 keeper which is constantly in metallic connexion is traversed 

 by alternating currents, which pass into each other at the azi- 

 muth 0° and 180°, and on account of the symmetrical distri- 

 bution of the whole, reach their maximum about the azimuth 

 90° and 270°t. 



If the intermittent spring is interrupted once at 90°, then the 

 secondary connexion which alone establishes the continuity in 

 the handles I and II, either by means of the body or some other 

 means of testing the current, receives the full intensity of the 

 positive current ; if it takes place twice during one whole revolu- 

 tion of the keeper, it receives two opposed currents in alternating 

 succession ; and if a voltameter be interposed, a mixture of oxy- 

 gen and hydrogen at both electrodes. This alternation can be 



• It is tlien fixed in a somewhat slanting position, so that it touches the edge 

 of the inlaid wood nearest to tiie keeper. 



+• On rapid revolution somewhat beyond that, when the sparks as well as the 

 shocks are most intense. 



