” varies slightly, both because of observational errors and because of Brownian movements. Under the column headed “

” are recorded the various observed values of the times of rise through 10 divisions of the scale in the eyepiece. A star (*) after an observation in this column signifies that the drop was moving with gravity instead of against it. The procedure was in general to start with the drop either altogether neutral (so that it fell when the field was on with the same speed as when the field was off), or having one single positive charge, and then to throw on positive charges until its speed came to the 6.0 second value, then to make it neutral again with the aid of radium, and to begin over again.

[TABLE XII]

Plate Distance 1.6 cm. Distance of Fall .0975 cm. Volts 1,015.
Temperature 230 C. Radius of Drop .000063 cm.

No. of Charges
on drop		No. of charges on
Ion Caught		No. of Charges
on drop		No. of charges on
Ion Caught
19.0100.01 P20.010.0*1 N
16.02 P1 P20.0*01 P
8.03 P1 P100.01 P1 P
20.0*01 P
20.016.02 P1 P100.01 P1 P
8.03 P16.02 P1 P
100.01 P
17.02 P1 P104.01 P
8.23 P1 P15.02 P1 P
6.04 P1 P9.03 P1 P
6.04 P
7.0*2 N
9.8*1 N1 P6.5*2 N
7.0*2 N10.0*1 N1 P
20.0*01 P
21.020.0*0100.01 P1 P
95.01 P1 P15.52 P1 P
16.52 P1 P8.03 P1 P
8.03.P1 P8.03 P1 P
6.04 P
100.01 P16.52 P
16.02 P1 P
8.43 P20.0*0
20.0106.01 P16.52 P
16.02 P1 P
8.43 P5.74 P
10.0*1 N100.01 P
20.0*01 P20.0*01 N
100.01 P1 P10.0*1 N1 N
16.02 P10.0*1 N1 N
100.01 P1 P
16.02 P1 P
8.03 P

44 catches, all singles

It will be seen from [Table XII] that in 4 cases out of 44 we caught negatives, although it would appear from the arrangement shown in [Fig. 12] that we could catch only positives. These negatives are doubtless due to secondary rays which radiate in all directions from the air molecules when these are subjected to the primary X-ray radiation.

Toward the end of [Table XII] is an interesting series of catches. At the beginning of this series, the drop was charged with 2 negatives which produced a speed in the direction of gravity of 6.5 seconds. It caught in succession 6 single positives before the field was thrown off. The corresponding times were 6.5*, 10*, 20*, 100, 15.5, 8.0, 6.0. The mean time during which the X-rays had to be on in order to produce a “catch” was in these experiments about six seconds, though in some instances it was as much as a minute. The majority of the times recorded in column