INDUSTRIAL PROGRESS DURING THE YEAR 1875. \\ 



rates of vibration of two sounding air columns by means of 

 oscillating flames. To the jets supplying two ordinary sing- 

 ing tubes are aflixed lateral branches, by which the gas from 

 each may also be supplied to a second burner supported on 

 a convenient lateral stand. When the flames in the tubes 

 sing, those outside vibrate in unison with them ; and by 

 means of a revolving mirror the ratio of the two may easily 

 be ascertained by counting. If the two singing flames are 

 connected to the same exterior flame, the combined vibration 

 is seen in the mirror. 



Tyndall, in a communication to the Royal Society on acous- 

 tic reversibility, discusses the curious results obtained at 

 Villejuif and Montlhery in 1822, when cannonading at the 

 latter station was heard at the former, but not the reverse, 

 and concludes that Montlhery must have been surrounded 

 by a highly diacoustic atmosphere, while Villejuif was in an 

 atmosphere acoustically opaque. He supports this position 

 by ingenious experimental evidence. 



Mercadier has printed a paper upon the law of the influ- 

 ence of the variation of the dimensions of a tuning-fork upon 

 its vibrations, in which he shows that the number of vibra- 

 tions is independent of the breadth, is directly proportional 

 to the thickness, and is inversely proportional to the square 

 of the length. From these laws it becomes possible to cal- 

 culate within one or two per cent, the dimensions of a fork 

 necessary to give any required number of vibrations. 



Neyreneuf has shown very beautifully the oscillatory or 

 vibratory character of the detonation of a mixture of oxygen 

 and hydrogen gases. In a tube the result may be shown in 

 two ways : either by making the tube perfectly dry inside, 

 in which case the watery vapor produced by the combustion 

 condenses preferably on the cooler parts of the tube, leaving 

 those parts transparent which the vibrating flame has heated, 

 or by coating the tube interiorly with a thin layer of par- 

 affin, when the melting of this substance shows the heated 

 portions. In these experiments it is necessary to graduate 

 the rapidity of the combustion to the size of the tube. With 

 a test-tube an inch and a quarter in diameter and eight inch- 

 es long, well dried, and filled with a mixture of equal vol- 

 umes of hydrogen and air, the stria? represented fern leaves. 

 With tubes of less diameter, the effects are more regular, es- 



