U2 



Dr. A. M. Tynclall on the Critical 



The two typical curves between rootpull and current are 

 shown in curves 3, designated A and B ; and the following 

 general statement may be made. 



Curves 3. 



PUfl 



3- 



2- 



Microamps 



14 



When the hemispherical end of the point is practically 

 covered with glow, the rootpull-current curve takes the 

 form A, showing that the field is independent of current in 

 such cases. This form is given in positive discharge in air 

 at atmospheric pressure, in both signs of discharge at com- 

 paratively low pressures, and in certain cases of negative 

 discharge in C0 2 . 



When the flow is trumpet-shaped and proceeds from a 

 relatively small area on the point, the rootpull-current curve 

 takes the form B. Negative discharge in air at atmospheric 

 pressure and certain cases of positive discharge in C0 2 

 furnish examples of this. With a glow of this form the 

 values of the field cannot be deduced from the pull with 

 great certainty, partly for reasons previously discussed under 

 the case of negative discharge in air, and partly because 

 discharge of this form is usually of an intermittent character. 

 It is not therefore possible to say whether the drop in root- 

 pull with increase of current indicates a true drop in field 

 or not. 



