Masterpieces of Science 



be termed telephonic currents of electricity. In 

 order that the peculiarities of these currents may 

 be clearly understood, I shall project upon the 

 screen a graphical illustration of the different 

 varieties. 



The graphical method of representing electrical 

 currents shown in Fig. i is the best means I have 

 been able to devise of studying, in an accurate 

 manner, the effects produced by various forms 

 of telephonic apparatus, and it has led me to the 

 conception of that peculiar species of telephonic 

 current, here designated as undulatory, which has 

 rendered feasible the artificial production of 

 articulate speech by electrical means. 



A horizontal line (g g') is taken as the zero of 

 current, and impulses of positive electricity are 

 represented above the zero line, and negative 

 impulses below it, or vice versa. 



The vertical thickness of any electrical im- 

 pulse (b or d), measured from the zero line, in- 

 dicates the intensity of the electrical current at 

 the point observed, and the horizontal extension 

 of the electric line (b or d) indicates the duration 

 of the impulse. 



Nine varieties of telephonic currents may be 

 distinguished, but it will only be necessary to 

 show you six of these. The three primary varie- 

 ties designated as intermittent, pulsatory and 

 undulatory, are represented in lines i, 2 and 3. 



Sub-varieties of these can be distinguished as 

 direct or reversed currents, according as the 

 electrical impulses are all of one kind or are alter- 

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