[6] See “La Nature,” 4th year, 1876, 2nd half-year, p. 167. M. A. Guillemin mentions, in connection with the phenomenon of July 12th, 1876, the presence of light masses of cloud of a greyish-blue colour, similar to those perceived in the phenomena just described.
[7] M. A. G. has written us an interesting letter on the subject of similar experiments, which we here transcribe:—
“When a siphon of seltzer water has been opened some little time, and the equilibrium of tension is nearly established between the escaped gas and the dissolved gas, a vertical stream of bubbles is seen to rise from the bottom of the apparatus, which present a very clear example of the law of ascension of bubbles; that is to say (putting out of the question the expansion of the bubbles in their passage upwards), it is an inverse representation of the law of gravity affecting falling bodies. The bubbles, in fact, detach themselves from their starting point with perfect regularity; and as the interval varies in one file from another, we have before us a multiplied representation of that terrible law which Attwood’s machine made such a bugbear to the commercial world. I believe it is possible, by counting the number of bubbles that detach themselves in a second, in each file, and the number which the whole stream contains at a given instant, to carry the verification further; but I must confess that I have not done so myself.”
[8] The experiment we have just described is a very old one. M. V. Sircoulon has told us that it was described at length in the works of Rabelais. The following remarks are in “Pantagruel,” book II., chap. xvii.
“Panuræ then took two glasses of the same size, filled them with water, and put one on one stool, and the other on another, about five feet apart, and placed the staff of a javelin about five-and-a-half feet long across, so that the ends of the staff just touched the brim of the glasses. That done, he took a stout piece of wood, and said to the others: “Gentlemen, this is how we shall conquer our enemies; for in the same way that I shall break this staff between these two glasses, without the glasses being broken or injured, or spilling a single drop of water, so shall we break the head of our Dipsodes, without any injury to ourselves, and without getting wounded. But that you may not think there is magic in it, you, Eusthenes, strike with this stick as hard as you can in the centre.” This Eusthenes did, and the staff broke in two pieces, without a drop of water being spilt.
[9] The curved surface of a column of liquid is termed a “meniscus,” from the Greek word meniskos, meaning “a little lens.”
[10] Traité de Physique, Paris 1874.
[11] Traité d’optique Physiologique. French translation by MM. Javal and Klein.
[12] From praxis, action, and skopein, to show.
[13] This interesting experiment, which we have exactly verified, was described to us by Professor Waldner, and M. A. Keppler.