PHYSICS. 



123 



that the character of the propagation of electric disturb- 

 ances of equilibrium is different according as the resistances 

 to be overcome are small or great ; (2) that with small re- 

 sistances such as that of 120 to 400 kilometers of copper 

 wire 2 millimeters in diameter restoration of the equilib- 

 rium takes place by oscillations, the amplitude of which 

 diminishes the more rapidly the greater the resistance; (3) 

 that with great resistances such as 1000 kilometers of the 

 above wire no oscillations are observed, the velocity being 

 inversely proportional to the total resistance and to the 

 length of the conductor, and hence, for two conductors of 

 equal specific resistance, being inversely as the square of the 

 length; and (4) that the velocity of electric signals magnet- 

 ically produced is not, except in cases where the resistance 

 is very large, comparable with that of disturbances of elec- 

 trical equilibrium, the latter being the greater. One curious 

 result the author draws from his investigation, i. e., that 

 when the resistance in the circuit is very small, the motion 

 of the electricity takes place almost exclusively upon the 

 outer surface of the conductor. 



W. Siemens has experimented to determine the velocity 

 of electric propagation. The two outer armatures of a con- 

 denser were connected together; the two inner ones, one to 

 the line, the other to a short wire. Both terminated in 

 points close to a revolving smoked cylinder. On putting 

 the arc connecting the outer armatures to earth, the con- 

 denser is discharged, and two sparks pass to the cylinder, 

 the difference between them indicating: the time of trav- 

 ersing the line. Siemens concludes that electricity has an 

 actual velocity of propagation. 



Sabine has proposed to use the time taken by a condenser 

 to discharge itself, or to pass from one potential to another, 

 through a circuit of known resistance, as a unit for measur- 

 ing very small intervals of time. 



Edison has discovered the fact that the conductivity of 

 graphite loosely compressed is remarkably increased by 

 pressure, probably from improved internal or external con- 

 tact. He has utilized this discovery in the construction of 

 his talking-telephone by placing such a cylinder of graphite 

 against the brass or mica diaphragm which receives the 

 sound and in the main circuit. The electrical current, which 



