and a saturating electromotive force of 600 volts was applied. The ionization current was sufficiently large to be measured by means of a sensitive high-resistance galvanometer, and readings were taken as quickly as possible after removal of the platinum from the emanation vessel. The initial value of the current (taken as 100) was deduced by continuing the curves backwards to meet the vertical axis (see Fig. 90), and was found to be 3 × 10-8 ampere.
| Time in minutes | Current |
|---|---|
| 0 | 100 |
| 2 | 80 |
| 4 | 69·5 |
| 6 | 62·4 |
| 8 | 57·6 |
| 10 | 52·0 |
| 15 | 48·4 |
| 20 | 45·4 |
| 30 | 40·4 |
| 40 | 35·6 |
| 50 | 30·4 |
| 60 | 25·4 |
| 80 | 17·4 |
| 100 | 11·6 |
| 120 | 7·6 |
These results are shown graphically in the upper curve of Fig. 90. The initial rapid decrease is due to the decay of the activity of the matter A. If the slope of the curve is produced backwards from a time 20 minutes after removal, it cuts the vertical axis at about 50. The difference between the ordinates