Nov. 16, 1882] 
NATURE 
ing from 120 to 150 horse-power to drive it, are capable 
of lighting from 1000 to 1300 incandescent electric lamps. 
Six such machines have been also erected in New York 
to supply the central station of the Edison Light Com- 
Fics. 2-5.—Sir W, Thomson’s Disk-Dynamo 
pany. Here the unexpected difficulty has arisen that if 
one of the machines drops in speed the currents from the 
other machines short-circuit themselves through the one, 
and overpower the steam-engine that is driving it ; a fault 
59 
| which \. ill probably be remedied by a rearrangement of 
the governors supplying the steam to the engines. 
New forms of dynamo-electric machine have been 
designed by Sir William Thomson, some of these being 
for direct currents, others for alternate, but all of them of 
peculiar construction. The first of them, shown in Fig. 1, 
may be described as a modification of Siemens’ well-known 
machine, the drum-armature being, however, made up like 
a hollow barrel, of which BB is a sectional view, the sepa- 
rate staves being copper conductors insulated from one 
another. They resemble the longitudinal bars used by 
Siemens in the armatures of his electro-plating machines, 
and by Edison in his steam-dynamo. At one end of the 
hollow drum these copper bars are united to each other in 
pairs, each to the one opposite it. At the other end their pro- 
longations serve as commutator bars. A similar mode of 
connecting to that adopted by Edison, is also possible. 
Inside this hollow drum armature is an internal stationary 
electro-magnet, KM’K, whose poles face those of the 
external field magnets. This internal magnet answers 
the purpose of intensifying the magnetic field, and making 
the magnetic system a “closed” one, as suggested long 
before by Lord Elphinstone and Mr. Vincent. This 
hollow armature Sir W. Thomson proposes to support on 
external antifriction rollers A A’ CC’, the lower pair AA 
being of non-conducting material, the upper pair being 
made up of conical cups of copper split radially, and 
serving, instead of the usual commutator “ brushes” to 
lead away the current. The hollow armature may be 
driven either by the tangential force of one of the 
bearing rollers, or by an aale fixed into the closed end 
of it. 
Another machine devised by Sir W. Thomson, and illus- 
Fic. 6.—Elevation of Gordon’s Dynamo, showing the rotating coils. The “taking-off” coi s are shown in the top right hendc rn >. 
trated in Figs. 2, 3, 4, and 5, is a disk-dynamo for generating 
alternate currents, and is therefore allied in certain aspects 
to Mr. Gordon’s machine, described below. The rotating 
armature has no iron in it ; it consists of a disk of wood 
having upon its sides projecting wooden teeth, as shown 
in Figs. 2 and 3, between which a wire or strip of copper 
is bent backwards and forwards, and finally carried to 
the axle B. This disk is rotated between field-magnets 
