the rollings after a considerable interval of time), we had been placed so that the original report had fallen on our ears nearly at the same moment as the echoes, we should probably have considered that the successive reports and rollings of the echoes were reports of successive explosions occurring nearly at the same moment, and that they were not echoes at all.
This is the only time (out of many storms witnessed in the Alps) I have obtained evidence that the rollings of thunder are actually echoes; and that they are not, necessarily, the reports of a number of discharges over a long line, occurring at varying distances from the spectator, and consequently unable to arrive at his ear at the same moment, although they follow each other so swiftly as to produce a sound more or less continuous.[1]
The wind during all this time seemed to blow tolerably consistently from the east. It smote the tent so vehemently (notwith-standing it was partly protected by rocks) that we had grave fears our refuge might be blown away bodily, with ourselves inside; so, during some of the lulls, we issued out and built a wall to windward. At half-past three the wind changed to the north-west, and the clouds vanished. We immediately took the opportunity to send down one of the porters (under protection of some of the others, a little beyond the Col du Lion), as the tent would accommodate only five persons. From this time to sunset the weather was variable. It was sometimes blowing and snowing hard, and sometimes a dead calm. The bad weather was evidently confined to the Mont Cervin, for when the clouds lifted we could see every-
- ↑ Mr. J. Glaisher has frequently pointed out that all sounds in balloons at some distance from the earth are notable for their brevity. "It is one sound only; there is no reverberation, no reflection; and this is characteristic of all sounds in the balloon, one clear sound, continuing during its own vibrations, then gone in a moment." (Good Words, 1863, p. 224.)
I learn from Mr. Glaisher that the thunder claps which have been heard by him during his 'travels in the air' have been no exception to the general rule, and the absence of rolling has fortified his belief that the rolling sounds which accompany thunder are echoes, and echoes only.
