THE POPULAR SCIENCE MONTHLY. 



conception is, it has been found by no means an easy one to* real- 

 ize in practice. The first one to attempt the application of this 

 principle to autographic transmission appears to have been Mr. 

 E. A. Cowper. In his apparatus, constructed in 1874, the receiv- 

 ing pen was mounted upon a light armature located between the 

 poles of two electro-magnets placed at right angles to each other. 

 These magnets were included in separate line circuits, and when 

 energized by currents from the transmitting end of the line, at- 

 tracted the pen armature, causing it to describe a line or curve 

 which was at every instant the resultant of the two right-angled 

 magnetic attractions. 



These magnetic attractions were varied in exact accordance 

 with the movements of the transmitting pen by augmenting and 

 diminishing the strength of the current flowing through the mag- 

 net coils, and this variation of current strength was in turn ac- 

 complished by causing contacts attached to the transmitting pen 

 to pass over the terminals of resistance coils and successively cut 

 out or introduce resistance in the line circuits. On account of 

 the very limited movements which could be given to both the 

 transmitting and receiving pens, the writing had to be done upon 



a strip of paper which 

 was moved under the 

 pen. The writing with 

 the transmitting pen was 

 done through a square 

 hole about an inch on a 

 side, and the characters 

 had therefore to be made 

 practically one over the 

 other. There was thus 

 but little opportunity for 

 the operator to follow 

 the work and see clearly 

 what he was doing, and 



only an expert could make an intelligible writing. The details of 

 this method were subsequently much improved by two American 

 inventors, and the apparatus employed for a time in commercial 

 work; but the essential limitations of the method proved too 

 serious a handicap, and the system soon fell into disuse. 



In taking the subject up experimentally Prof. Gray at first 

 used the method of a variable resistance, but he speedily aban- 

 doned it as impracticable, and adopted the step-by-step method of 

 operation, which he now uses. This cgnsists in causing the trans- 

 mitting pen to send to the line a succession of distinct electrical 

 impulses, the number of which is governed by the extent of the 

 pen's movement, which are employed, not in affecting the receiv- 



FIG. 13. TELAUTOOKAPH TRANSMITTER. 



