556 



Prof. H. L. Callendar on Electrical 



axilla on consecutive nights. The curve is often very smooth 

 during sleep, but becomes irregular owing to greater rest- 

 lessness on awaking. These accidental excursions seldom 

 exceed a few tenths of a degree, unless the patient gets out 

 of bed, and are chiefly due, in all probability, to slight dis- 

 placements permitting intrusion of air betwen the thermo- 

 meter and the skin. In the record shown in fig. 10 a very 



Fig. 10. 



38° 



37" 



36 c 



% < 4 6 



Axillary Thermometer C, fastened in 



with adhesive wax. 



smooth curve was obtained by sticking the thermometer to 

 the skin with adhesive wax. Unfortunately this record was 

 of shorter duration, only six hours, and, as the patient did 

 not get to bed until 2.30 A.M., it is possible that excessive 

 fatigue may have induced unusual soundness of sleep. 



Recording Instruments. 



7. Two principal types of recording instruments are avail- 

 able, corresponding respectively to the Deflexion Method, 

 and the Balance Method of measuring variations of electrical 

 resistance. In the deflexion method, the greater part of the 

 resistance to be measured is balanced on a Wheatstone bridge 

 by a balancing coil, and the small variations are observed by 

 the deflexion of the galvanometer. In the balance method, 

 the galvanometer contact is moved along a bridge -wire 

 until balance is obtained. This method is not so quick for 

 small variations, but is generally most suitable for work 

 with resistance thermometers, and has the advantage that 

 the scale is uniform and independent of the E.M.F. of the 

 battery. In clinical thermometry, the range of temperature 

 to be covered is so small that the deflexion method is 

 generally applicable and the scale practically uniform. The 

 scale is readily adjusted to read in degrees of temperature 

 by means of a suitable rheostat in the battery circuit. If 

 storage cells of sufficient capacity are employed there is 



