52 



THE ROYAL SOCIETY OF CANADA 



changes in the substance not accounted for by the classical theory. 

 To avoid circumlocution the two legs of the tube will be spoken of as 

 the liquid side and the vapour side. The liquid side is the one which 

 is full of liquid or contains all of the liquid at ordinary temperature. 

 The vapour side contains no liquid at ordinary temperature. 



Three sets of readings are taken at any temperature or at any 

 time and the mean of the three decrements is taken as the value for 

 the observations. The temperatures are taken from calibrated ther- 

 mometers and are probably correct within -1°. The platinum resis- 

 tance thermometer is used as a check on the steadiness of the tempera- 

 ture in the heater. In the first part of the work the temperatures are 

 held constant for about half an hour before the readings of the swings 

 of the pendulum are taken. In the constant temperature work 

 readings are taken at intervals of about half an hour and are continued 

 long enough to indicate the trend of the curve. In observing the swings 

 of the pendulum it was found easier on the whole to read alternate 

 maxima and quite as satisfactory. So this was usually done except 

 when the decrement is very small and then every fifth and in some 

 cases every tenth swing was observed. 



RESULTS. 



As has been mentioned, the earlier attempts at determination 

 of the decrement were made by counting the number of swings of 

 the pendulum cylinder while the amplitude decreased from a certain 

 value to a definite fraction of that value. The method was found 

 unreliable, particularly when the decrement is small, since it is then 

 impossible to tell which swing takes the pendulum nearest a given posi- 

 tion. One is very apt to get a value which accords with preconceived 

 notions. The results will be discussed under two headings. Under 

 the first are those where the change in the decrement with the change 

 in the temperature is shown and under the second those in which time 

 changes are shown. The following table gives necessary data con- 

 cerning tubes and cylinders: — 



