250 
THE TELEGRAPH . 
an hour. On account of the nature of the apparatus, it 
requires the services of a skilled mechanic at the places where 
it is used, but as it is used only on the great lines, such 
mechanics abound in cities like Paris, Lyons, and Marseilles. 
A form of telegraph apparatus that in America has super¬ 
seded every other non-recording instrument, and in England 
is now largely used by the Post Office instead of the Morse 
instrument, may here be particularly mentioned. The prin¬ 
ciple of it is indicated on a preceding page, and even a form 
of the apparatus described, as the reader will find by referring 
to the tenth and eleventh paragraphs of Chapter II., Part I,, 
pages 25 and 26. The simplest form of the instrument consists 
of an electro-magnet through which the line or the relay cur¬ 
rents pass. The armature of the electro-magnet is attached to 
a metallic bar that oscillates on a pivot. A spring causes the 
farther extremity of the bar to press against an adjustable 
peg, and in this position the armature is a little above the 
iron core of the electro-magnet. The moment the current 
passes the armature is attracted, the action of the spring 
is overcome, and the bar turns until it strikes, with a sharp 
click, another metallic point which is so adjusted ' that the 
armature is then not quite in contact with the magnetized 
iron bar. When the current ceases, the spring again brings 
back the bar into contact with the upper peg, with a sound 
which in general is readily distinguishable from the former one, 
or may easily be made so, and which the ear of the telegraph 
operator recognizes as the end of the signal, that is, the 
instant when the contact is broken at the transmitting key. 
It is the varying length of the contacts forming the dash and 
dot of the Morse alphabet, that are read by the sounds, almost 
as fast as the clerk can write the message down in words. 
There are, of course, various modifications of the “ sounder,” 
for the purpose of re-inforcing the sound, &c. The advan¬ 
tages of the instrument are its comparatively small cost, 
which is less than one-third of that of the Morse recorder ; 
the smaller charges for maintaining in working order; and 
lastly—a matter of great importance in practical telegraphy— 
its more rapid rate of working, for more words can be trans¬ 
mitted by it than by any other form of telegraphic instru¬ 
ment. 
