THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 139 



The thermal junctions are indicated in the upper left-hand corner by 

 the numbers i, 2, and 3. In No. i there are four subdivisions corre- 

 sponding to the four sections top, upper zone, lower zone, and bottom 

 of the metal walls of the chamber. No. 2, which is here indicated as 

 in series with No. i, represents the thermal junctions in the air cur- 

 rent. No. 3 represents the four subdivisions of the system of thermal 

 junctions in the inner and outer air-spaces. 



The resistance thermometers for indicating temperature changes in 

 the air of the chamber and the copper wall are represented by the coils 

 5,7, and R. These are here shown to be connected so as to have one 

 common return. The coil W represents a resistance thermometer for 

 measuring differences in temperature of ingoing and outgoing water 

 for heat absorption. (See p. 149.) 



All the above connections terminate in the mercury switch at the 

 rear of the center of the table. Extending backward from this are 

 two wires leading to the galvanometer. 



In the upper right-hand corner of the table is the rheostat controlling 

 the heating circuits. No. i represents the four circuits in the different 

 sections of the inner air-space and No. 3 the circuits for the corre- 

 sponding sections of the outer air-space. The 32-candlepower lamp is 

 that used in heating the ingoing air. The switch in the upper right- 

 hand corner of the diagram connects the rheostat with the city electric 

 main. 



On the lower right-hand corner are wires leading to a storage bat- 

 tery. The binding posts numbered 3, 4, 5, and 6 are for connections 

 for electric check tests and for magnetization of the fields of the bicy- 

 cle ergometer. 



MERCURY SWITCH AND BRIDGE. 



In order to keep the two metal walls of the chamber adiabatic, each 

 thermal junction system i. e., those corresponding to the top, upper 

 zone, lower zone, and bottom is connected so that the differences in 

 electro-motive forces of the junctions in thermal contact with the zinc 

 and the copper walls can be measured on the galvanometer and thus 

 furnish an indication as to whether the zinc wall should be warmed or 

 cooled. Similarly, the four outer thermal junction systems in the inner 

 wooden wall are so connected that they may be put in series with the 

 galvanometer. Not only are the individual sections of these two ther- 

 mal junction systems thus connected, but the wiring is such that the 

 algebraic sum of the electro-motive forces of the junctions in all four 

 sections may be noted for each system ; consequently there are five 

 connections necessary for each system, /. e. , the four parts and the 



