206 RECORDING. 



3. Automatic contact. A pin G, which projects from the edge of 

 the drum disc, strikes against a wire H once in the revolution of the 

 drum. This wire is so bent as to allow the pin to pass in either 

 direction. In setting the contact it must be made as short as possible, 

 so that the make and break shocks which are produced may be fused 

 into one stimulus. 



One contact in a revolution is sufficient for the purposes of these 

 exercises, but another arrangement can be substituted which allows of 

 single or successive stimuli at different intervals. 



Recording* arms and points. Thin wooden rods 2 mm thick 

 armed at one end with an aluminium point A of the accompanying 

 pattern, the actual end of which consists of a glass thread 1 cm long. 

 Its end is glazed to perfect smoothness in a small flame, and is then 

 attached by cement. 



B 



FIG. 35. H Hi age. A Writing point. B Silk double loop. 



Two pieces of the wooden rod, one 22 cm and the other 8 cm long 

 are inserted into the outer holes of the hinge piece of the muscle- 

 chamber and held together with thread as in the figure. 



This arrangement is light, strong, and possesses great horizontal and 

 vertical rigidity, the necessary play being provided by the aluminium 

 point. 



Attachment of the muscle to the recorder. Tie a piece of silk thread 

 (Fig. 35, B) (fine plaited roach line is best) into two loops each 2'5 cm 

 long, the whole not to exceed 6 cm in length 



Draw the knots tight to prevent stretching. 



Fasten one end to the lever by placing one loop round the latter 

 and passing the other through it and draw it tight. 



Let the thread rest at such a distance from the hinge that the 

 movement of the point shall magnify the movement of the muscle four 

 or five times. 



Pass the other end through the hole in the floor of the muscle- 

 chamber and slip it over the hook on the tendon. 



Covering 1 the drum. Take a sheet of the ready cut glazed paper 

 from the tin on the shelf of the varnishing table (Fig. 36) and lay it, 



