electromagnetic momentum which coincides with the direction of the system and which is contained in the cavity, we have to calculate expression (1) with , then to integrate with respect to from O to , and then to multiply the result with the volume of cavity . If we additionally substitute for its value[1], then the momentum becomes
Now, the longitudinal electromagnetic mass is given by ;[2] thus it becomes equal to (when higher terms are neglected):
This is half of the value given by me.
After it was sought in vain after a principal difference, I found that this difference stems from a calculation error, unfortunately committed by me in my paper. At p. 362, line 6 from above,
not shall be stated, but ,
therefore the heat absorbed by the walls of the cavity when the system is accelerated, is:
however, since furthermore the walls have given off the heat , we can say that the walls of the cavity (when accelerated by ) have altogether given off the heat