THE NEW ELECTKO-MAGNETIC MACHINES. 
287 
lever is balanced at the other end by a heavy weight. When 
the induction-coil is fully charged, its magnetic attraction will 
drawdown the keeper, and the contact of a platinum point with 
a cup of mercury is broken at the opposite end of the lever, a 
bright flash being emitted. The accumulation of electricity 
again goes on in the induction-coil until the keeper end of the 
lever is again depressed, contact broken at the opposite weighted 
end, and the flash repeated ; and so on continuously. By means 
of clock-work arrangement, and an excentric plate • dipping 
periodically into the mercury contact, the transmission of the 
current from the land machine can be delayed for definite 
intervals, and by such periods, combined with the intermittent 
flashes, the beacon can be made to optically speak its name in 
unmistakable terms and to convey its needed warning to every 
mariner. The commissioners of Northern Lights and some of 
the authorities connected with the Southern Lights have already 
entertained the project. 
Professor Wheatstone has also proposed a similar method for 
the direct conversion of dynamical into electrical force founded 
on the like gradual augmentation of the slightest polarity into 
a powerful magnet. The construction of Mr. Wheatstone’s 
model is this. The case of the electro-magnet is a plate of soft 
iron 15 inches in length and half an inch in breadth bent into 
a horse-shoe form and coiled round by 640 feet of insulated 
copper (-jL-th inch) wire. Within it is a rotating Siemens arma- 
ture 8J inches long, coiled longitudinally with 80 feet of wire 
like that on the electro-magnet. Professor Wheatstone shows 
the existence of an energetic current by heating 4 inches of 
platinum wire *0067 inch diameter. This heating power is 
obtained by making a short circuit through the wire and is 
temporarily of great intensity but quickly subsides; and a 
current can then only be maintained equal to keeping one inch 
of the wire at a red heat. 
Mr. Ladd’s first model consisted of two plates of soft iron 
(A, B) about 7^ inches in length, 2J inches in breadth, and \ 
inch thick, placed horizontally, with a Siemens rotating arma- 
ture between them at each end (EE, HH). Over each of these 
plates about 30 yards of insulating wire (No. 10) is coiled 
[kkk k). The armature at one end ( h h) acts in connection 
with a magnet or piece of soft iron, having a slight quantity of 
residual magnetism. The current from this armature charges 
the electro-magnet (ab). The second armature (ee) at the 
other end of the electro-magnet takes off the electricity which 
is conveyed by copper wires to two fixed terminals (s s), whence 
it is applied to the practical purpose required. The power of 
this little model is very great, and sufficient to maintain three 
inches of platinum wire (*01 inch diameter) at a white heat. 
VOL. vi. — NO. XXIV. Y 
