410 THE POPULAR SCIENCE MONTHLY. 



iu four cases out of five, if not in a larger proportion, the sciences are 

 impropei'ly taught, by inferior or incompetent men, and therefore, as 

 means of education, fall into disrejjute. The classics have less rigor- 

 ous 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 meth- 

 ods or by improperly-trained teachers. The two systems, being so 

 diiferent, 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. 



Br JOHN TYNDALL, F. E. S. 



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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 Montlhery, both lying south 

 of Paris, and 11.6 miles distant from each other. Prouy, Mathieu, and 

 Arago, were the observers at Villejuif, while Humboldt, Bouvard, and 

 Gay-Lussac, were at Montlhery. 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 Mont- 

 lhery was heard with the greatest distinctness at Villejuif, by far the 

 greater number of the reports from Villejuif failed to reach Montlhery. 

 Had wind existed, and had it blown from Montlhery 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 Montlhery, 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 Mont- 

 lhery was heard d merveille [with wonderful distinctness] at Villejuif, 

 but one shot out of twelve fired at Villejuif was heard, and that fee- 

 bly, at the other station. 



