ELECTRICITY AT THE WORLD'S FAIR. 



53 



Fig. 14. TELAUToriBAPH Eeceiveb. 



ing pen directly, but in controlling the mechanism which actuates 

 it. As the extent of movement of the pens is determined only 

 by the number of electrical impulses, these may be given any 

 desired range, and it becomes possible to use the transmitting pen 

 with almost the same freedom as a pen or pencil in ordinary 

 writing, and to write in the same way that is, in successive 

 lines extending across a page. 



In the final form given to the instruments by Prof. Gray and 

 shown at the exposition the transmitter consists of a box provided 

 with a leaf upon which 

 the paper rests. The pa- 

 per is drawn continu- 

 ously from a roll, and 

 is shifted mechanically 

 from time to time by the 

 operator. The writing 

 pen consists of a pencil 

 lead mounted in a holder, 

 to the lower end of which 

 two silk threads are at- 

 tached. These threads 

 are at right angles to 

 each other, and lead from 



the pencil to two drums, upon which they are wound in such a 

 manner as to cause the drums to rotate backward and forward 

 a,s the threads follow the movement of the pencil point. The 

 drums, therefore, move in exact accordance with the rectilin- 

 ear components of the pen's motion, and it is only necessary to 

 reproduce their motions at the other end to cause the receiving 

 pen to duplicate the movements of the transmitting one. In an 

 earlier form of the transmitter each drum carried an arm, which 

 was swept by its movement over a series of radial electrical con- 

 tacts, and thus sent a succession of electrical impulses to line. 

 The friction of this moving arm was, however, found to be objec- 

 tionable, and this arrangement has therefore been replaced by a 

 magnetic device in which a toothed iron disk acting magnetically 

 upon a soft iron lever keeps this in vibration. This lever plays 

 between two contact points, and according as it is upon one or the 

 other of the contacts a positive or negative current impulse is sent 

 by a battery through the line circuit. These current impulses 

 of alternating polarity serve to operate at the receiver polarized 

 relays, which control by means of escapements drums similar to 

 those in the transmitter, which drums actuate the receiving pen. 



This pen consists of a glass tube drawn to a capillary bore at 

 the end and supplied with a free-flowing ink from a reservoir by 

 m.eans of a rubber tube. It is mounted upon and at the junction 



