MAGNETISM AND ELECTRICITY. 169 
immediately vanishing on breaking the connexion of one wire. A third 
wire passes from the place where the battery is situated to the third post, c, 
placed on the same board with a and b; the extremities of the coil wound 
around the right-hand horse-shoe pass to b and c, so that this can be 
rendered alternately magnetic or not. In front of the poles of the right 
horse-shoe is an iron plate, moving backwards and forwards on two pins at 
its lower end ; to this is fastened a vertical beam, carrying above the cross- 
piece d. When the horse-shoe becomes magnetic it attracts the iron ; on losing 
this magnetism the attraction ceases, and a weak spring pressing against 
the beam throws it off again. In this manner a backward and forward 
motion of the cross-piece, d,is effected. At each end of the latter is a small 
ball which strikes a little bell at every backward and forward motion, conse- 
quently a person standing at the battery can make signals through the bell. 
The left horse-shoe has a similar plate, with a beam carrying the cross-piece 
rs. At each end of the cross-piece are pieces which catch alternately in the 
teeth of a twelve-toothed wheel in such a manner that at each backward and 
forward motion of the iron plate the wheel is moved forward one tooth. 
The axis of the toothed wheel passes through the centre of a disk of sheet 
iron, to which also the bell is fastened. Upon the borders of this disk (in 
our figure on the face opposite to the spectator) twenty-four signals are 
painted at equal distances, viz. twenty-three letters of the alphabet (exclusive 
of X and Y), and a point. An index on the same side of the disk, carried 
by the axis of the toothed wheel, is by the rotation of the latter moved 
forward one letter at each opening or closing of the circuit. When the 
index is set to the point (.). closing the circuit carries it to A, opening it 
again to B, &c., consequently an operator at the battery can make the index 
point to any letter on the disk, making a signal with the bell when the letter 
intended is reached. To avoid any error here, an apparatus is applied close 
to the battery, to regulate the opening and closing of the circuit: p and n 
are the two poles of the battery ; from p an insulated copper wire passes to 
the brass post, 6, of the recording apparatus; from the negative pole, x, 
there passes a shorter wire to the post, /, of the regulating apparatus. On 
this apparatus, besides /, there are two other posts, m and q, into which the 
Wires coming from a and ¢ are screwed. Communication is established 
between / and the brass spring tu, not visible in the figure. On pressing 
this down it touches a button projecting from g, and the current 
passes from p through 3, c, q, 4, to m, the current thus being closed. Let 
the spring tu fly back again and the current is broken, the circuit being 
opened. 
A second brass spring proceeding from the post J, when not depressed, 
touches a button on m, and thereby closes the circuit, so that the current 
from the positive pole passes through }, a, m, /, to the negative pole, 2, of 
the battery. Depressing the spring of course interrupts the current. Over 
the middle of the last mentioned spring there is a disk turning about a hori- 
zontal axis, Im whose circumference are inserted twenty-four rods or 
spokes, alternately long and short. Of these, one of the larger ones is 
ot3 
