CHRONOGRAPH. 209 



most convenient. The apparatus consists of (1) the time giver and (2) 

 the repeater, or style, which writes upon the recording surface. 



For the purpose of supplying a number of workers simultaneously 

 the following device is adopted in this laboratory : 



A time distribution board is placed against the wall, which consists 

 of a clock, the pendulum of which beats seconds. In the case below 

 are a tuning fork which oscillates 96 times and a spring oscillating 

 10 times a second. 



Both the latter are kept in action by independent Leclanche 

 batteries (one quart cell to each, two are available in case of need). 



The clock, fork, and spring control a main table circuit, which 

 consists of a battery of ten Leclanche cells, the leads of which branch 

 to the tables, where they terminate in fixed binding screws. 



A worker at any of the tables can, after connecting an electric 

 style to the binding screws of his table, select any of the above time 

 fractions by placing the plug which corresponds to his table number 

 into the brass bar of the time board. 



The accompanying diagram explains the method. 



Electric style. Chronograph. This consists of an electro-magnet,, 

 to the armature of which a writing point is attached. The latter is 

 drawn away from the magnet by means of a spring, the tension of 

 which is overcome whenever the current passes through the coil. The 

 core of the latter is made short and of electrolysed iron, so that it. 

 shall have no magnetic memory, i.e., will demagnetise the moment the 

 current ceases to flow through it. 



The form used is Smith's style, which possesses the great advantage 

 of having a low resistance, its coils being wound in parallel and in 

 having its armature placed at the end of a comparatively long arm. 

 The result is that it possesses a quick response and the "lost time" is 

 very short, even though comparatively small electrical power be employed. 



Muscle chamber. (Fig. 34.) A wooden floor, with a glass cover, 

 having a screw nut underneath for attachment to a bracket P on the 

 pillar of the general stand. 



A brass upright pierces the floor and carries within the chamber a 

 clamp for holding the femur of a muscle preparation, and beneath a 

 hinge-piece to which the writing arm is fixed. These are adjustable 

 vertically and laterally. Care should always be taken to set the arm 

 horizontally at the commencement of a record. 



Inside the muscle chamber are also platinum and non-polarisable 

 electrodes upon a horizontal bar, not shown in the figure. 



General stand. (Fig. 34.) A heavy foot supports an upright, to 

 which a stout pillar of steel N is pivoted between centres. 



