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THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Aet. XI. — Researches in Acoustics ; by Alfred M. Mayer. 



f Paper No. 10 containing The Variation of the Modulus of Elasticity with 

 Change of Temperature as determined by the Transverse Vibration of Bars at 

 Various Temperatures. The Acoustical Properties of Aluminum. 



[Read before the British Association, at Oxford, Aug., 1894.] 



Summary of the Research. 



Poisson in his Traite de Mechanique (Paris, 1833, t. II, 

 pp. 368-392)* discusses the laws of the transverse vibrations 

 of a bar free at its ends and supported under its two nodes. 

 He shows that the frequency of the vibrations of the bar is 

 given by an equation, which, reduced to its simplest expression, 



is IS" = Yx 1*0279-^; in which N" is the number of vibrations 



per second of the bar, t its thickness, I its length and Y the 

 velocity of sound in the direction of the length of the bar. 



To ascertain how near the frequency of the transverse vibra- 

 tions of a bar, computed by Poisson's formula, agrees with the 

 result obtained by experiment, the following method of experi- 

 menting was used. 



Rods of steel, aluminum, brass, glass and of American white- 

 pine (Pinus strobus) — substances differing greatly in their 

 moduli of elasticity, densities and physical structures — were 

 carefully wrought so as to have the length of 1*5 =fc meter ; the 

 thickness of 0*5 cm , the width of 2 cms , and a uniform section 

 throughout their lengths. The velocity of sound in these rods 

 was determined by vibrating them longitudinally at a tempera- 

 tute of 20°, while held between the thumb and forefinger, and 



*See, also, The Theory of Sound, by Lord Rayleigh, 1894, vol. i, ch. 8. 

 Am. Joue. Sci. — Fourth Series, Vol. I, No 2. — February, 1896. 



