42 



CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



GALVANOMETER 



about the left-hand solenoid back through a 600-ohm resistance to the main 

 line. The use of the 110-volt current under such circumstances would nor- 

 mally produce a notable sparking effect on the pointer P, and to reduce this 

 to a minimum there is a high resistance, amounting to 10,000 ohms on each 

 side, shunted between the main line and the creeper connections. This 

 shunt is shown in diagram in fig. 22. Thus there is never a complete open 

 circuit and sparking is prevented. 



THE CLOCK. 



The clock requires winding every week and is so geared as to move the 

 paper forward at a rate of 3 inches per hour. The contact-point for open- 

 ing the circuit T on fig. 22 is likewise connected with one of the smaller 

 wheels of the clock. This contact is made by tripping a little lever by 

 means of a toothed wheel of phosphor-bronze. 



INSTALLATION OF THE APPARATUS. 



The whole apparatus is permanently and substantially installed on the 

 north wall of the calorimeter laboratory. A photograph showing the vari- 

 ous parts and their installation 

 is given in fig. 23. On the top 

 shelf is seen the galvanometer 

 and on the lower shelf the re- 

 corder with its glass door in 

 front and the coordinate paper 

 dropping into the box below. 

 The curve drawn on the co- 

 ordinate paper is clearly shown. 

 Above the recorder are the re- 

 sistance-boxes, three in num- 

 ber, the lower one at the left 

 being the resistance S^, the 

 upper one at the left being the 

 resistance S', and the upper 

 one at the right being the re- 

 sistance Zj_. Immediately above 

 the resistance-box Z x is shown 

 the plug resistance-box which 

 controls on the one hand the 

 resistance r and on the other hand the resistance S, both of which are sub- 

 stantially altered when changing the apparatus to register from the to 4 C 

 scale to the to 8 scale. A detailed wiring diagram is given in fig. 24. 



1 1 O v D.C. 



FIG. 24. Detailed wiring diagram showing all parts of 

 recording apparatus, together with wiring to ther- 

 mometers complete, including all previous figures. 



