112 ANNUAL OF SCIENTIFIC DISCOVERY. 



atmosphere lias full time to flow into the ground, and Hughes's machine 

 may be operated without danger to the attendants, during a storm which 

 stops all the others. To accomplish this, the magnet is made of a natural 

 horse-shoe magnet capable of sustaining five pounds, in contact with the 

 poles of which are placed two pieces of soft iron, surrounded by coils of 

 wire. The armature is provided with a spring nearly as strong as the mag- 

 net, the tendency of which is to pull them apart. When the machine is at rest 

 the armature is in contact with the pieces of soft iron where it is kept. As 

 these have become magnetic from their contact with the natural magnet, 

 when a key is pressed down the current is made to pass through the coil in 

 such a direction as to destroy the natural magnet by creating an artificial 

 one with poles reversed. The armature is thus instantaneously let free, and 

 is thrown up by the spring; this motion acts upon a detent, and the other 

 parts of the instrument do their office in transmitting a letter, and also of 

 cutting off the current from the magnet and of forcing back the armature 

 against it. In this manner the natural magnet is not required to attract tho 

 armature from a distance, but acts only, when in contact, to hold it in its 

 place; that is, in the position of its greatest power. The parts of the 

 machine which are in constant motion consist of a horizontal main shaft 

 under which is a vertical shaft, connected with the first by beveled wheels- 

 of a train of cog-wheels, of a drum, weight, spring and treadle. The main 

 shaft of the instruments at both extremities of the line move with exactly 

 the same speed. The velocity of each is regulated, like that of a common 

 clock, by an anchor escapement, with this difference, that the vibrations of 

 a slender bar of steel, held by one extremity, are substituted for the beats 

 of a pendulum. A clock is made to go slow or fast by lengthening or short- 

 ening the pendulum, and the velocity is regulated here by doing the same 

 with the bar of steel. This escapement acts about sixty times in a second, 

 or tAventy times faster that that of a clock; and this result could not be 

 obtained from a pendulum, as this would have to be only 1-80 part of an 

 inch long from the point of suspension to the centre of the ball, to beat 

 sixty times. The upper portion of the vertical shaft is isolated from the 

 lower portion by an intermediate piece made of ivory. Tho upper part 

 is provided with an articulated horizontal ami which rests on a shorter 

 arm extending from the lower part, and this contact connects together 

 the two portions of the shaft. This arm describes circles a quarter of 

 an inch above the table. Under its extremity a circular row of twenty- 

 ei^ht slats is cut in the table, and as many metal slides are placed 

 vertically in them. Twenty-eight keys are connected with these slides, 

 in such a manner that, when a key is pressed down, the corresponding 

 slide is raised in the slat sufficiently high to reach the arm, which, in 

 revolving, slides up the inclined end of the slide. This operation makes 

 the current pass through the coils of the other instrument, as will be shown 

 hereafter. The main shaft carries by friction a type-wheel, the types of 

 which are inked by a small tangential inking roller. A second horizontal 

 shaft moving with the first, but faster, is provided with a chuck, by means 

 of which it carries the printing shaft once round each time a letter is tele- 

 graphed. This printing shaft, by means of a projecting cam, brings at each 

 turn the roller which carries the paper in contact with the type-wheel, and 

 the letter actually there is printed. The slip of paper is carried onward tho 

 distance of a letter by a dog acting on a ratchet, when the roller recedes from 

 the type-wheel, 



