354 



PHYSICAL EXPRESSION. 



minal, k, is fixed to the main bracket. Increase 

 of air-pressure in the tambour raises one end of 

 the beam, e, and depresses the other, d, which thus 

 comes in contact with its insulated wire /, com- 

 pleting a circuit through the terminal i ; diminished 

 air-pressure allows the beam to move in the oppo- 

 site direction, completing a circuit through the 

 terminal h. 



The instruments are made for me by Mr. W. 



Fig. 51 .Electrical Counter. 



Groves, 89, Bolsover Street, W. The electrical 

 counter (Fig. 51) consists of a clock, to the pen- 

 dulum of which a small piece of soft iron, c, is 

 attached, opposite an electro-magnet, d. In use for 

 counting the movements of a finger, the conducting 

 tube (Fig. 50, I) from the finger is attached to 

 the electrical contact-making tambour. One pole 

 of a Leclanche' battery of four cells is connected 



