Stress and Strain on the Properties of Matter. 



Fig. 1. 

 A B 



screwed on again ; whilst at the other extremity of the envelope was 

 an aperture, C, finch in diameter, through which a thermometer could 

 be inserted so that its bulb would lie along the axis and in the centre 

 of the coil of wire. 



The envelope served a double purpose, as it not only enabled com- 

 pensation to be made in the manner presently to be described for loss 

 of heat during the transference of the wire from the air-chamber to 

 the calorimeter, but also was of use in distributing the heat uniformly 

 throughout the coil, which was not the case when no such precaution 



Fig. 2. 



was taken.* The thermometer was placed in the air-chamber in a 

 position which was nearly horizontal, but slightly slanting upwards 

 so as to prevent the column of mercury in the thermometer tube from 

 being broken when the temperature was falling. As soon as the coil 

 of wire had attained the desired temperature, the calorimeter was 



* In- some preliminary experiments made without the envelope I frequently found 

 a difference of quite 1° between the temperature of the centre of the coil and that of 

 one end, but with the envelope there was, after a certain interval of heating, no 

 sensible difference of temperature. 



