Nov. 22. I9I5 Improved Respiration Calorimeter 327 



the tubes is tightly closed at each end, the leads from the resistance wire 

 being carried out through a small tube attached to the tube surrounding 

 the wire. As in the flat-type thermometer, this small tube terminates in a 

 bulb containing phosphorus pentoxid, to keep the annular space free from 

 moisture. The cylindrical shell inclosing the resistance wire is mounted 

 in a brass tube which provides a water channel so designed that the water 

 flowing in it passes inside the inner and outside the outer of the tubes in- 

 casing the wire, which is thus brought into intimate contact with all the 

 water flowing through the thermometer, and responds instantly and ac- 

 curately to changes in its temperature. Because of the design of the ther- 

 mometer and the manner in which it is mounted in the walls of the cham- 

 ber, the usual fluctuations of the temperature of the air adjacent to the 

 case of the thermometer introduce no error in the measurement of the 

 temperature of the water flowing in the bulb. One of these thermome- 

 ters is placed in the incoming water pipe so that it will be at the tempera- 

 ture of the water just as it passes through the copper wall, and the other 

 is similarly placed in the outgoing water pipe. 



The two thermometer coils are in the corresponding arms in opposite 

 branches of the circuit of a special Wheatstone bridge (PI. XXXV, fig. 2), 

 which may be accurately balanced for inequalities in resistance of the 

 coils as small as 0.00 1 ohm and as large as i ohm, resulting from a differ- 

 ence of o.oi degree and of 10 degrees, respectively, between the tempera- 

 ture of the water entering and that of the water leaving the heat absorber. 

 The total resistance of the slide wire of the bridge will compensate for an 

 inequality of 0.2 ohm in the resistance of the coils which results from a 

 difference of 2 degrees in their temperature. If there is no difference in 

 the temperature of the water in the two thermometers, the bridge is bal- 

 anced with the battery circuit contact at the low end of the wire, while if 

 the temperature of the water leaving the heat absorber is 2 degrees higher 

 than that of the water entering it, the bridge is balanced when the contact 

 is at the upper end of the wire. To compensate for inequalities due to 

 temperature differences greater than 2 degrees, eight coils of manganin 

 wire in series are arranged so that any number of them may be connected 

 in series with the slide wire, thus shifting the position of the contact on the 

 wire at which the bridge may be balanced and altering the significance of 

 the balance point in temperature difference. The lower end of the wire 

 may thus be made to correspond to any whole number of degrees of tem- 

 perature difference between o and 8, with the upper end 2 degrees higher 

 in each case. The coil and slide wire are joined by means of a heavy cop- 

 per link, with one end in the mercury cup in which one end of the slide 

 wire terminates and the other end in a similar cup in which an end of the 

 extension coil terminates. 



The slide wire of the bridge is incorporated in a mechanism (PI. XXXV, 

 fig. 2) which automatically balances the bridge for inequalities of resist- 



