The following remarks may give some explanation of the phenomenon of alternating currents in this cave, I should suppose that during the night there is atmospheric equilibrium in the cave itself, and in the three pits A, B, C. When the heat of the sun comes into operation, the three pits are very differently affected by it, C being comparatively open to the sun's rays, while A is much less so, and B is entirely sheltered from radiation. This leads naturally to atmospheric disturbance. The air in the pit C is made warmer and less heavy than that in A and B, and the consequence is, that the column of air in C can no longer balance the columns in A and B, which therefore begin to descend, and so a current of air is driven from the cave into the pit C. Owing to the elasticity of the atmosphere, even at a low temperature, this descent, and the consequent rush of air into C, will be overdone, and a recoil must take place, which accounts for the return current into the cave from the pit C. The sun can reach A more easily than B, and thus the air is lighter and more moveable in the former pit, so that the recoil will make itself more felt in A than in B: accordingly, we found that the main currents alternated between A and C, with very slight disturbance in the neighbourhood of B. B will, however, play its part, and the weighty column of air contained in it will oscillate, though with smaller oscillations than in the case of A. Probably, when the sun has left A, while acting still upon C, the return current from C will be much slighter, and there will be a general settling of the atmosphere in the pits A and B, until C also is freed from the sun's action, when the whole system will gradually pass into a state of equilibrium.
Cruel comme à Morat was long a popular saying.
See p. 258.
Acta SS. Bolland. May 9.—If possessed of the characteristics of his race—'tall and proud'—his activity belies the first line of the old saying,
Bibl. Univ. de Genève, First Series, xxi. 113. See also Edinburgh Philosophical Journal, viii. 290.