APPENDIX A. 310 



(7) The base may be clamped to a support and the 



tracing point adjusted to any height or direction. 

 This simple chronograph may be made sufficiently deli- 

 cate to record ^-seconds accurately, though seconds or 

 half seconds will usually answer the purposes of the gen- 

 eral experiment. For very small divisions of a second the 

 tuning fork should be used. 



To set up a simple chronograph. Join the chronograph 

 and the contact clock or a metronome in continuous circuit 

 with a common Daniell cell. The clock makes contact 

 every second or fraction, the armature is drawn down by 

 the electro-magnet and thus records the time upon the 

 drum of a kymograph. 



16. The chronographic system. 



If many students are working at the same time and at 

 the same experiment in a laboratory, it is unnecessarily 

 costly in both money and space for each student or group 

 of students to be supplied with separate chronographic 

 clocks and batteries. One clock and a battery of several 

 cells can be employed to run ten or twelve chronographs. 

 Such a chronographic system is too simple to require ex- 

 tended description. 



(1) Bowditche's interruption clock or Petzold's simple 

 contact clock may be hung in any convenient place in 

 the laboratory and brought into circuit with 



(2) A battery, in series, whose strength must depend 

 upon the amount of external resistance to be overcome, 

 i. e., the number of chronographs in the system. 



(3) The chronographs must be all in one general circuit 

 rather than upon branches from a primary circuit. 



(4) A loop of the general circuit may pass to each 

 table and the chronograph inserted in the loop. It is 

 hardly necessary to remind the demonstrator that if, 



