Electric Waves passing through Telegraph Lines. 325 



time ; I will therefore give here a brief description of its me- 

 chanical construction. On the base a is (supported by pillars) a 

 bridge, b b, in the middle of which is pivotted a brass disk with 



Fia - . 3. 



heavy rim (d d). At e' a band-spring is fixed which reaches to e, 

 and at that end carries a catch centred on a pin. A small screw- 

 head in the rim of the disk engages with this catch, and by means 

 of it the spring may be forced backwards until a second pro- 

 truding screw-head reaches the trigger/, by which it is locked. 

 On releasing the trigger, the spring (recovering its position of 

 rest) accelerates the disk until it is arrested against the con- 

 tact-stud g, at which point it stops, whilst the disk is free to 

 continue its revolution. The tension of the spring and posi- 

 tion of the trigger are adjustable in order to " time " the period 

 of revolution. On the top of the disk and turning with it is 

 an arm, h, whose position is fixed by a clamp, h' . This arm 

 is furnished with a protruding finger, i. In front of the board 

 which carries the disk is a second board, k, which carries a 

 small contact-key, I, working between contact-studs in and n, 

 and retained indifferently against either of them by means of 

 a spring at the side. The periphery of the disk is divided into 

 500 equal parts, the zero-point being in such a position that, 

 the nonius on the arm h being placed coincident with it, the 

 finger i just touches the insulated face of the key I (at rest on 

 m) when the end of the spring e touches the contact-stud g. The 

 arm h being placed in any other position and the disk released, 

 the interval of time which elapses between the closing of contact 



