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THE POPULAR SCIENCE MONTHLY.

in four cases out of five, if not in a larger proportion, the sciences are improperly taught, by inferior or incompetent men, and therefore, as means of education, fall into disrepute. The classics have less rigorous needs, the proper teachers are more easily obtained, and thus they carry off a glory which is not rightfully theirs.

It is safe to say, in conclusion, that the new education will contrast unfavorably with the old only when it is imparted by incorrect methods or by improperly-trained teachers. The two systems, being so different, can hardly be compared upon the same ground. Let each do its own work, in its own way, with truly equal advantages, and, beyond a reasonable doubt, the new education will show the more vigor. Its greater utility, its wider range of discipline, and its more varied adaptability to dissimilar minds, unite to give it wonderful advantages.

 

ON THE MOTIONS OF SOUND.
By JOHN TYNDALL, F. R. S.

I.—ACOUSTIC REVERSIBILITY.

ON the 21st and 22d of June, 1822, a commission appointed by the Bureau of Longitudes of France executed a celebrated series of experiments on the velocity of sound. Two stations had been chosen, the one at Villejuif, the other at Montlhéry, both lying south of Paris, and 11.6 miles distant from each other. Prony, Mathieu, and Arago, were the observers at Villejuif, while Humboldt, Bouvard, and Gay-Lussac, were at Montlhéry. Guns, charged sometimes with three pounds of powder, were fired at both stations, and the velocity was deduced from the interval between the appearance of the flash and the arrival of the sound.

On this memorable occasion an observation was made which, as far as I know, has remained a scientific enigma to the present hour. It was noticed that while every report of the cannon fired at Montlhéry was heard with the greatest distinctness at Villejuif, by far the greater number of the reports from Villejuif failed to reach Montlhéry. Had wind existed, and had it blown from Montlhéry to Villejuif, it would have been recognized as the cause of the observed difference; but the air at the time was calm, the slight motion of translation actually existing being from Villejuif toward Montlhéry, or against the direction in which the sound was best heard.

So marked was the difference in transmissive power between the two directions that on the 22d of June while every shot fired at Montlhéry was heard à merveille [with wonderful distinctness] at Villejuif, but one shot out of twelve fired at Villejuif was heard, and that feebly, at the other station.