196 Mr M c Glung, Investigation of the effect of Temperature 



independent of any variation which might take place in the 

 testing cylinder AB. The charge imparted to E, which is propor- 

 tional to the amount of ionization produced in the gas between 

 the plates E and E', was indicated by the deflection of the 

 electrometer needle. This reading being taken, the electrometer 

 quadrants were discharged and then the charge contained in / and 

 the condenser C was thrown into the electrometer by insulating 

 the quadrants and closing the key W, and the deflection corre- 

 sponding to the charge in / was observed. Several of these 

 readings at any given temperature were taken and then the mean 

 taken of each set. 



The first sets of observations were taken by measuring the 

 ionization at the ordinary temperature of the room and then 

 heating the cylinder and contained air up to a given steady 

 temperature and again measuring the ionization at that tempera- 

 ture. Then it was again heated to a still higher temperature and 

 the ionization was again measured, and so on to the highest 

 temperature observed. To take measurements at several tempera- 

 tures over a range of about 200° occupied considerable time, and 

 it was found that by reversing the order and heating to the 

 highest temperature first and then cooling down step by step, the 

 observations could be obtained in much less time and that the 

 experiment could be worked more satisfactorily. It is desirable 

 to take the observations as quickly as possible, for the liability of 

 variations of the X-ray bulb and of other conditions is lessened by 

 shortening the length of time occupied by a series as much as 

 possible. The latter order of taking the readings was therefore 

 adopted in the later experiments. 



Results of experiments. 



The first test was made of course with air. Several series of 

 readings were made with the cylinder filled with air, and it was 

 found that for a range of temperatures of nearly 200° C. there was 

 no change in the amount of ionization produced in the air when 

 its temperature was altered. Observations were taken at several 

 temperatures from about 14° C. to a little over 200°, and the 

 ionization was found to remain constant over this range of 

 temperature. A sample series of results obtained for air is given 

 in Table! 



Although the above readings are not absolutely constant, still 

 any apparent variation is quite within the limits of experimental 

 error and the agreement is really very good considering the varia- 

 tions which usually take place in the working of a Rontgen ray 

 bulb. Each of the numbers given above represents the mean of 

 several observations. The above results show without doubt that 



