170 PHYSICS. 
indicated by a point, the others are indicated by letters of the alphabet in 
their proper succession, as in the recording apparatus. 
The figure represents the apparatus at the time when a message is about 
to be transmitted. The operator, by depressing the spring tu, gives by 
means of the bell a signal of warning to the operator at the other station. 
He then turns the wheel so that the short spoke marked A is vertically 
underneath. The spring dm immediately flies up, and the circuit is closed, 
thus causing the index at the other station to point to A. Moving the 
wheel again until the long spoke marked B is underneath, the circuit will be 
broken, and the index of the recording apparatus will point to B. In this 
manner the operator continues until he comes to the letter to be signalized, 
when the other spring is touched and the bell rung to indicate that the 
proper letter has been reached. The index of the one apparatus and the 
wheel of the other are then to be brought back again to the point (.), to 
begin afresh with the next letter. 
Figs. 41 and 42, pl. 22, represent the working part of Steinheil’s electric 
telegraph, laid down by him in 1837 between his residence in Munich, the 
physical cabinet of the Academy building in that city, and the Royal 
Observatory in Bogenhausen, near Munich, a distance of 37,000 feet. The 
conductor consisted of three portions : 30,500 feet of copper wire between 
the Academy and the observatory, carried through the air and stretched 
over the steeples of the city ; 6000 feet of iron wire between the Academy 
building to Steinheil’s dwelling-house and back again, likewise carried 
through the air; and 1000 feet of copper wire in the Academy building 
itself, extending to the machine-shop of the physical cabinet, carried along 
the joints of the floor, and partly embedded in masonry. The exciting 
apparatus, instead of being a yalvanic battery as in the preceding 
telegraphs, is a Clarke’s magneto-electric machine. This consisted of a 
compound horse-shoe magnet of seventeen plates of hardened steel, 
weighing, when armed, sixty pounds, and possessing a power of 3000lbs. 
The reversal of the current is effected without a commutator by the 
turning of the inductive coils in the opposite direction. The momentary 
connexion of each conducting wire with the magneto-electric battery 
moves a horizontal balancer, ending in two metal balls, which need only be 
moved to the right or left to give the signs. To prevent the mercury from 
being spilled by the hooks in the rapid rotation of the multipher, a 
cylindrical glass ring (pl. 22, fig. 41) is placed over the mercury vessel. 
Small magnetic bars, sixty millimetres long, ten high, and eight broad, are 
used for making the signs; they are fixed by twos, one in the prolongation 
of the other, in the frame of a multiplier interpolated in the circuit. In 
either direction of the current only one of the magnets can be moved. At 
the inner and contiguous extremities of these bars are small vessels 
running out into horizontal beaks with capillary apertures. When these 
vessels are filled with a fluid oil black, the extremities will leave the 
impression of a point on a strip of paper, moved along by clock-work, with 
which they are brought into contact. This paper is prepared for use by 
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