i§ 77 *J Recent Advances in Telegraphy. 373 
M. la Cour provides, by means of eledtro-magnets, that the 
fork shall be maintained constantly in a state of vibration. 
In either case the current sent into the line by depressing 
the signalling-key is interrupted by the fork an equal number 
of times per second that the fork vibrates. This intermit- 
tent current traverses the line to the distant station, where 
it is passed “ to earth ” through the receiving apparatus 
shown in Fig. 12. This consists of a fork similar to the 
first, and vibrating the same note. Each leg is surrounded 
by a helix of wire. Two other helices are placed upright, 
one on each side of the ends of the legs ; they are fitted 
with iron cores, and adjustible poles, n, s, and are in fadt 
eledtro-magnets. These four helices are joined up in series, 
so that the line-current passes through each in turn. It 
magnetises oppositely the legs of the fork, which are at- 
traced by the contiguous poles of the eledtro-magnets. 
The legs of the fork are thus pulled apart, and let go with 
each pulsation of the intermittent current. In this way the 
fork is put into audible vibration. 
These vibrations are also turned to the adtual recording 
of the message in permanent marks, by means of a local 
circuit and Morse or other recorder. A fine metal point, p, 
is brought very near to one leg of the fork, so that when the 
fork vibrates this leg comes into contadt with the point, and 
completes the local circuit through the fork, local battery, 
and recording instrument. 
M. la Cour’s first experiments were made in June, 1874, 
on a short line in the neighbourhood of Copenhagen, and in 
November of the same year he succeeded in working 
