If, however, the summit of the primary column succeeds in breaking off (as in Fig. 18b), or even in very nearly breaking off, then the impact of this newly-formed drop forms a second slight crater on the top of the first cake, and we have the series (18b to 24b), in which it will be observed that the rim of the secondary crater spreads rapidly outwards, so that a second well-marked circular ripple in this case quickly follows the first. The secondary column that is thrown up in Fig. 23b is very like that which emerged at a much earlier stage in the (a) series.
The photographs of this (b) series show very beautifully the manner in which the advancing edge of the ripple degenerates into smaller ripples travelling with greater speed.
SERIES I—(continued)
Alternative (b).
| 18b 0·214 sec. |
| 19b 0·237 sec. |
| 20b 0·242 sec. |
| 21b 0·244 sec. |