APPENDIX A. 



317 



tograph. As used by the draftsman such an apparatus 

 enlarges figures by any multiple from 1 to 5 in linear di- 

 mensions, for that purpose the tracing stilus is placed at 

 a and the recording pen or pencil at b, while the point c is 

 fixed to the table. As used to trace the curvature of any 

 line in the body, the recording pencil is fixed at , while 

 the point b is made to follow the curved surfaces under 

 observation. In this way records of one-fifth the linear 

 dimensions of the curve traced may be recorded. Such rec- 

 ords are compact and readily filed for subsequent reference. 



\\ 



14. The pneo=manometer. 



This instrument may be easily con- 

 structed in the laboratory. Take a piece 

 of heavy glass tubing of 7 to 9 mm. lumen 

 and at least 160 centimeters in length. 

 Bend it as shown in Fig. 61. A covered 

 filter may be attached as shown in the 

 figure if there is any tendency for the 

 mercury to be thrown out. 



15. The chronograph. 



For many experiments, especially upon 

 the circulation or respiration, it is neces- 

 sary to trace upon the rotating drum, along 

 with the record of the circulatory or respi- 



\ratory movement, a record of time in 

 seconds or known fractions thereof. In- 

 struments for this purpose are to be had 

 from the instrument houses. 



If the student or demonstrator is in- 

 clined to construct his own chronograph 



the accompanying figure and description 

 The Pneo-mano- \ * 



meter. For test- may be of assistance to him. (See Fig. 

 ing pressure in Q^.'] 

 forced respiration. 



FIG 61. 



