86 A. M. Mayer — Researches in Acoustics. 



The method of Chladni, used exactly as that eminent man 

 used it, remains the best we have. It is important, however, 

 to note that the rod must be held between the thumb and 

 forefinger when it is vibrated and not clamped when vibrated. 

 When clamped it always gives a higher frequency, as shown 

 by the following experiments : 



Steel rod clamped 3429-2 Aluminum rod clamped 3377-0 



Steel rod held between fingers 3428-4 Aluminum rod held between fingers 3376-4 



The frequency of the vibrations of the rods of steel, brass, 

 aluminum, glass and pine wood, when held at the middle of 

 their lengths and vibrated so as to give their fundamental 

 tones, gave exactly the octaves of these fundamental tones 

 when held at one-quarter of their lengths and vibrated. 



Determination of the lengths of the long rods and of the lengths 

 and thicknesses of the bars. 



The lengths of the rods of l*5db meters were ascertained 

 by comparison with the rod of steel whose length was meas- 

 ured at the Bureau International des Poids et Mesures. The 

 lengths and thicknesses of the bars which were vibrated trans- 

 versely were measured with micrometer calipers. The read- 

 ings of these calipers were tested by comparison at 20° with a 

 series of standards of various lengths of inches and fractions 

 of inches, made for me with great care by Mr. George M. 

 Bond, who has charge of the gauge department of the Pratt, 

 Whitney Co. In reducing the comparisons to centimeters I 

 adopted the value of the inch as equal to 25*4 millimeters. 

 In obtaining the length of a bar, the mean of several measures 

 in the axis of the bar and in directions parallel to the axis and 

 at various distances from it was adopted. The thickness of a 

 bar was taken as the mean of measures taken throughout the 

 length of the bar at points designated by the intersections of 

 lines drawn parallel and at right angles to the axis of the bar. 



The dimensions of the bars were measured at 20°, except 

 those of steels Nos. 3, 4, 5, which were measured at 18°*25. 



Determinations of the Coefficients of Expansion of the Bars. 



To determine the coefficients of expansion of the bars I 

 devised the apparatus shown in fig. 2. In a brass tube, T, the 

 bar, B, rests in slots in the supports, S, S'. The tube, T, is 

 slightly shorter than the bar, B. Washers of rubber (shown 

 in black in the figure), of the same diameter as the outside 

 diameter of the tube, are placed in the screw-caps, C, C 

 These washers are perforated with holes of diameters smaller 

 than the thickness of the bar. When the caps are screwed up 



