148 A RESPIRATION CALORIMETER. 



two heavy copper terminals, which can be dipped in the iron mercury- 

 cups. Four of these coils, corresponding to the four bridge systems, 

 are shown immediately in front of the switch in figure 40. They are 

 shown in position in figure 41. The terminals of the coil for system 

 No. 5 are slipped through two hard-rubber bushings hi the cover, and 

 extend beneath the cover far enough to have their lower ends well 

 immersed in mercury in two iron cups similar to those used for the 

 galvanometer terminals. Those for system No. 5 are at the left and 

 near the top of the switch, as shown in figure 40. A line terminating 

 in arrow-heads and broken by the designation No. 5 shows in figure 43 

 the position of these cups and the connections with their lower ends. 

 The iron mercury-cups, as well as the iron posts for the battery and 

 bridge connection previously mentioned (see p. 143), are provided on the 

 under side with hexagonal nuts, which are used to insure the best elec- 

 trical contact for the various parts of the bridge system. These nuts 

 and the wiring from several of the iron cups and posts are shown in 

 figure 42. As can be seen by a comparison with the direction of the 

 bundle of wires extending outward from one side, the switch has been 

 tipped forward through 180 from the position in figure 40 to give the 

 view in figure 42 ; consequently the three nuts at the bottom of figure 

 42 correspond in figure 40 to the two galvanometer terminal mercury 

 cups and the iron post connecting with the battery. 



Although the hexagonal nuts aid in making a good contact, the con- 

 nections for all the bridge systems, especially the connections which, if 

 defective, would disturb the equilibrium of either arm of the bridge, 

 are further insured by having soldered joints. All connections between 

 the iron mercury-cups and the calorimeter chamber are made of very 

 heavy (No. 10) copper wire to eliminate the effect of temperature 

 fluctuations other than those in the thermometer coils. 



The key controlling the temperature measurements of the copper 

 thermometers which indicate the temperature of the copper wall, No. 

 7, is in the bottom row (fig. 43), at the extreme right. The compari- 

 son coil dips in two iron cups filled with mercury. These cups are at 

 the right of the switch, in a position corresponding to that occupied by 

 the comparison coil No. 5. The line terminating in arrow-heads is 

 broken by the designation No. 7. 



The key marked R controls the temperature measurement of a cop- 

 per coil used for obtaining the rectal temperature of the subject of the 

 experiment. This thermometer is described in detail elsewhere. (See 

 p. 156.) The comparison coil for R is immediately at the left of the 

 keys A I, I, No. i and No. 5. 



