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POPULAR SCIENCE REVIEW. 
0*017 inch diameter, the usual wire for ordinary large coils 
being No. 35, diameter 0’008 inch. The current from the 
intensity-armature of Mr. Wilde’s machine was sent through 
the primary wire, the induction current being then shown across 
the points without any condenser being used. The current was 
sent from the big armature for a few seconds only, Mr. Ladd 
being naturally afraid of damage to his instrument. The re- 
sult was a perfect arc of flame which, if measured in its full 
high bend, would be at least 4 inches, the carbon points attached 
to the terminals being 2 inches asunder. When a platinum 
break was used with this coil for but an instant, the combustion 
was so great that with about a dozen flashes it so fused the ends 
of the platinum rods as to make the distilled water in which 
they were immersed like ink with the solution of the metal. 
Mr. Wilde’s magnificent machine is a practically accomplished 
fact, and we are glad to know that a 7 -inch apparatus is about 
to be set to work for the Commissioners of Northern Light- 
houses. 
We have next to consider the several other important models 
and propositions. The first of these is the proposal by Mr. 
Siemens to take the electrical force direct from the electro- 
magnet without any previous separate charging by a distinct 
magneto-electric machine. Mr. Siemens has found that after 
imparting the slightest magnetism to an electro-magnet — and 
there is always sufficient residual magnetism for the purpose — 
the armature can be made to intensify it and to impart at each 
revolution a higher charge to the magnet, thus absorbing at each 
turn more and more magnetism and returning a more and more 
intensified current into the magnet, causing in this way, by its 
own action, an incessant augmentation of force until the power 
of the magnet would become sufficient to arrest the action of 
the machine by overpowering the force employed to drive it, or 
by heating the coil around it to a degree that would injure the 
insulating cover of the wire. 
Mr. Siemens’ machine consists of a battery of electro-magnets, 
within which a coiled armature is rapidly rotated in the same 
way as within Mr. Wilde’s large electro -magnet, the difference 
in the two machines being that Mr. Siemens’ periodically and 
alternately charges and discharges the accumulated magnetism, 
whilst Mr. Wilde continuously withdraws the full electric force 
from his electro-magnet and as constantly refurnishes the electro- 
magnet with electricity by a separate magnetic machine acting 
independently but simultaneously. Mr. Siemens proposes to 
utilise his invention by conveying the current from the machine 
ashore by a submarine cable to beacons and light-vessels afloat, 
on board which it will be accumulated and intensified in a 
suitable induction-coil. A keeper attached to one end of a 
