A. 31. Mayer — Researches in Acoustics. 105 



The fact that aluminum gives, from a comparatively slight 

 blow, a great initial vibration and that its vibrations last for a 

 short time, render this metal peculiarly well suited for the 

 construction of those musical instruments formed of bars 

 which are sounded by percussion and the duration of whose 

 sounds is not desirable. 



I had hopes that the aluminum would prove to be a good 

 substance out of which to make plates on which to form the 

 acoustic figures of Chladni. Experiments have shown that 

 aluminum is not suited to this purpose. I had plates of 

 aluminum carefully cast, with 2 cms of thickness. These 

 plates were turned down on the face-plate of a lathe to thick- 

 nesses of 2 mm and 3'8 mm . Three of these plates were quite hom- 

 ogeneous in elasticity, for the Chladni figures when obtained on 

 them were symmetrical. Yet the Chladni figures were diffi- 

 cult to produce, because it is difficult to obtain a pure tone 

 from an aluminum plate. The sound is generally more or less 

 composite ; therefore, the plate in its vibration tends to form 

 two or more figures at the same time, and the consequence is 

 that either no figure is formed or one is given that is not 

 sharply defined. One square plate of 30*8 cms on the side and 

 •38 cm thick, gave quite clearly the three following tones : UT 3 

 (1), SOL a (2), and SOL 4 (3). Corresponding respectively to 

 the Chladni figures of (1) two lines drawn from opposite 

 points of the center of sides of plate ; (2) figure formed of the 

 two diagonals drawn from the corners of plate ; (3) figure sim- 

 ilar to (1) but with corners of plate cut off by curved lines. 

 Fig. 4 corresponded so nearly to the sound of SOL 4 that a 

 vibrating SOL 4 fork when held near the plate set the latter 

 into vigorous vibration. 



Another difficulty met with in using plates of aluminum for 

 Chladni's figures is that sand, even when entirely free of salt 

 and of the globular grains of wind-blown sand, does not move 

 freely over a vibrating surface of aluminum, whether this 

 surface has been polished or has been slightly tarnished and 

 roughened by the action of alkali. 



There is one serious objection to the use of aluminum in the 

 construction of musical and acoustical instruments, and that is 

 the great effect that the change of temperature has upon its 

 elasticity. If a bar of aluminum and a bar of cast-steel be 

 tuned at a certain temperature to exact unison, a change from 

 that temperature will affect the frequency of vibration of the 

 aluminum bar 2-J- times as much as the same change of tem- 

 perature will affect the bar of cast- steel. 



