Dr. A. M. Mayer's Researches in Acoustics. 195 



The fact that aluminium 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. 



1 had hopes that aluminium 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 

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

 aluminium 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 homogeneous in elasticity, for the Chladni figures when 

 obtained on them were symmetrical. Yet the Chladni figures 

 were difficult to produce, because it is difficult to obtain a pure 

 tone from an aluminium plate. The sound is generally more 

 or less composite ; therefore the plate iii its vibration tends to 

 form two or more figures at the same time, and the con- 

 sequence 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 2 (1), SOL 2 (2), and SOL 4 (3). Cor- 

 responding respectively to the Chladni figures of (1) two 

 lines drawn between opposite points of the centre of sides of 

 plate; (2) figure formed of the two diagonals drawn between 

 the corners of plate ; (3) figure similar to (1) but with corners 

 of plate cut off' by curved lines. Figure 3 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 vibrat on. 



Another difficulty met with in using plates of aluminium for 

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

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

 move freely over a vibrating surface of aluminium, 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 aluminium in the 

 construction of musical and acoustical instruments, and that 

 is the great effect that change of temperature has upon 

 its elasticity. If a bar of aluminium and a bar of cast-steel 

 be tuued at a certain temperature to exact unison, a change 

 from that temperature will affect the frequency of vibration 

 of the aluminium bar 2^ times as much as the same change of 

 temperature will affect the bar of cast-steel. 



