192 Mr. Watkins on Electro-magnetic motive Machines. 



in the lower cistern, and then connected with the mercury 

 cups g^ gf which answer for top and bottom cisterns. The 

 ends of the copper wire coils of each pole are judiciously joined 

 by solder to two pendent platinum wires, and form the ends 

 of each system of the electro-magnets, as shown in the plate. 

 Now when the points of the pendent platinum wires impinge 

 upon the surfaces of the mercury in two partitions placed side 

 by side, a current passes along the wire coils, and gives a po- 

 larity of a certain kind to all the four poles of the soft iron 

 magnets, and those of an opposite kind to the adjacent poles 

 of the fixed permanent magnets are attracted by the latter; 

 but after they have arrived opposite the fixed magnets, they 

 pass a barrier, and a change takes place in the direction of 

 the current by the pendent wires again impinging on two sur- 

 faces of mercury : that in the inner surface is now in connexion 

 with a different electrode to what it was before, it being in the 

 same condition as the outer one was in the first instance; and, 

 vice versa, the outer partition is in connection with the elec- 

 trode which in the first instance was in the same condition as 

 the inner. The order of the polarity in the soft iron is in- 

 fluenced by the direction of the electric current pervading the 

 system of coils. It is therefore easy to conceive how the 

 polarity of the soft iron may be reversed when the direction 

 of the current is changed, provided, as elsewhere has been 

 observed, this reversal is within certain limits of time. 



This alternate attraction produces the revolution of the 

 electro-magnets. The lower system of electro-magnets is 

 at an angle as regards the upper system ; so that when one 

 system is in a position in which it operates most powerfully, the 

 other system is at the dead point or nearly so ; by this ar- 

 rangement the systems assist each other over that difficulty. 

 On the metal vertical shaft is a bevel toothed wheel k, which 

 gears into another bevel wheel on a horizontal shaft /, which is 

 (Carried away and made to produce motion, and work at a di- 

 stance small pieces of machinery, such as models of tilt hammers, 

 pumps, dredging machines, &c. A plain pulley may be affixed 

 to the vertical shaft, and with a long band made to operate ; 

 by this means the friction of the bevel gear is saved. 



k, ky/c, a mahogany base for the whole instrument. 



Fig. 2. This is another form of model of an electro-mag- 

 netic motive machine: «, a, a, a, a mahogany board; b, b, Z>', Z>', 

 two soft iron electro-magnets with their bent parts underneath 

 the board ; c, c, c', c\ and d, d, d', d'^ are four flat bent per- 

 manent steel magnets, arranged like the arms of a windmill, 

 and attached to a norizontal moveable axis, which is supported 

 on a hollow wooden column e. 



The arrangement of the axis could not be shown in the 



