Recording Thermometers for Clinical Work. 557 



little risk of error from variation of the E.M.F. of the battery. 

 Thus, for clinical thermometry, there is little to choose 

 between the balance and deflexion methods, if the instru- 

 ments employed in either case are equally sensitive. In the 

 installation of underground thermometers, buried at various 

 depths in the soil at McGill College in 1894, the deflexion 

 method was employed, as being the quickest, for the daily 

 readings of each thermometer ; but the balance method was 

 adopted, as being the most accurate, for taking continuous 

 records of the diurnal variations when occasion required. 

 In order to obtain a strictly continuous record by the de- 

 flexion method it is necessary to employ photography, but 

 a practically continuous record may be obtained, as in the 

 Thread Recorder made by the Instrument Co., Cambridge, 

 by depressing the pointer attached to the galvanometer coil 

 so as to mark its position on the record sheet by means of 

 an inked thread at regular intervals of a minute, the index 

 being free for the greater part of the time. For records of 

 long duration the separate dots coalesce into a continuous 

 curve if the variations are not too rapid. 



Adjustment and Use of the Thread Recorder. 



8. The standard type of Thread Recorder is a fairly robust 

 instrument, having a resistance of about 10-12 ohms, and a 

 scale of 80 mm. to one millivolt. With a Copper-Constantan 

 thermocouple, this instrument gives a scale of about 3 mm. 

 to 1° C, which is rather too small for clinical records. With 

 a resistance thermometer, it is easy to get a scale of 50 mm. 

 to 1° C. if desired, but a scale of 10 to 20 mm. is usually 

 suflicient. 



In using the thread recorder with a resistance thermo- 

 meter, some form of platinum thermometer bridge with a 

 slide-wire is required, and a rheostat or resistance box capable 

 of fine adjustment between 30 and 50 ohms. This rheostat 

 is connected in series with a 2 volt storage cell to the battery 

 terminals (marked B on the bridge), and serves to adjust the 

 scale of the record. The thread recorder is connected to 

 the terminals marked G on the bridge, one of which is con- 

 nected between the equal ratio coils of 10 ohms each, and 

 the other to the sliding contact on the bridge-wire, as shown 

 on the diagram, fig. 11 (p. 558). 



The two thermometer leads are not connected to the 

 terminals marked P on the bridge (which is the usual 

 arrangement when the balance method is used), but to the 



