Recording Thermometers for Clinical Work. 559 



of the bridge-wire, or ten units o£ the plug resistances R, 

 will correspond to a tenth of an ohm, or 1° C, on the 

 thermometer. 



To adjust the galvanometer scale, the thermometer may be 

 placed in a vessel of water at the temperature of the room, 

 and the bridge balanced. If the temperature is 15° 0. 

 (which is 25° 0. below 40° C.) it will be necessary to unplug 

 250 units (equivalent to 25°) in the box at R to balance S, 

 when the sliding contact is at zero in the centre of the bridge- 

 wire. If balance were obtained with 230 units in R, and 

 the sliding contact at 7*3 cm. to the right of zero, it would 

 mean that the temperature of the water was 40 — 23 + *73 

 = 17 0, 73 C. In any case, to obtain a fine adjustment for the 

 balance, the sliding contact must be shifted till the galvano- 

 meter shows no deflexion, and then clamped in position. 

 The galvanometer being thus balanced at a steady tempe- 

 rature, increase the resistance unplugged in R by 50 units 

 (0 - 5 ohm), corresponding to a rise of temperature of 5° C. 

 on the thermometer. If the adjustment of the rheostat is 

 •correct the galvanometer should deflect 5° to the left, i. e. to 

 the extreme left of the record sheet. If the galvanometer 

 deflects to the right the connexions of its terminals must be 

 reversed. If the deflexion is less than 5°, the resistance of 

 the sliding rheostat must be reduced, and vice versa, until 

 the desired deflexion is obtained. The adjustment will then 

 be correct for any temperature within the range of the 

 instrument up to 40° C. To get a range on the record sheet 

 from 35° to 40° C, for records of normal body temperature, 

 it would then be necessary to unplug 50 units in R and to 

 set the bridge-wire contact at zero, so that the zero of the 

 galvanometer scale may correspond to 35° C. Similarly for 

 a range from 40° to 45° C, the resistance unplugged in R 

 should be zero. Temperatures above 45° could be measured 

 by increasing the balancing resistance S, but it is not 

 advisable to go above 45° C. with celluloid thermometers. 



The accuracy of adjustment of the thermometer and its 

 balancing coil S can be tested at any time by immersing the 

 thermometer either in melting ice, or in water at the room 

 temperature if a reliable mercury thermometer is available. 

 If, for instance, the galvanometer reads zero when the ther- 

 mometer is in water at 17°'67 0. with 230 units unplugged, 

 and the contact at 73 mm. (reading 17°* 73 C), the thermo- 

 meter reads 6 mm. or '06° C. too high at this temperature, 

 -and the error may be corrected by setting the bridge-wire 

 contact 6 mm. to the right of zero for the record, instead of 

 at zero. Several different thermometers may be used with 



