Prof. A. M. Mayer's Researches in Acoustics. 523 



to one fourth the amplitude of that curve and by taking wave- 

 lengths corresponding to the intervals indicated below the 

 figures. 



All the curves which I have given in this paper were first 

 drawn on a large scale and then reduced by photography to a 

 size suitable to be transferred to the engraver's block. 



7. Experiments in which are produced from the above curves 

 (Section 6) the Motions of a Molecule of Air when it is ani- 

 mated with the resultant action of the six elementary vibrations 

 forming a musical note, or is set in motion by the combined 

 action of sonorous vibrations forming various musical intervals. 



We may imagine the curve corresponding to a musical note, 

 represented in fig. 3, as formed by the trace of a vibrating mole- 

 cule of air, or of a point of the tympanic membrane, on a sur- 

 face which moves near these points. Therefore, if we slide this 

 curve along its axis under a slit in a screen which allows only 

 one point of the curve to appear at once, we shall reproduce in 

 this slit the vibratory motion of the aerial molecule and of 

 the point on the tympanic membrane. I have exhibited this 

 motion in a continuous or, rather, recurring manner as follows : — 

 On a piece of Bristol board I drew a circle, and in one quadrant 

 of this circle I drew five hundred equidistant radii. On these 

 radii, as ordinates, I transferred the corresponding values of the 

 same ordinates of the resultant of fig. 3, diminished to one fourth 

 of their lengths. I thus deflected the axis of curve, fig. 3, into 

 one fourth of a circle-curve ; and this repeated four times on the 

 Bristol board, rendered the curve continuous and four times re- 

 curring, as shown in fig. 7. I now cut this curved figure out 

 of the board and used it as a template. I placed the latter cen- 

 tred on a glass disk 20 inches in diameter. The disk was 

 covered on one side with opaque black varnish ; and with the 

 template and the separated points of a pair of spring dividers I 

 removed from the glass disk a sinuous band, as shown in fig. 7. 

 The glass disk was now mounted on a horizontal axis and placed 

 in front of a lantern the diameter of whose condensiug-lens was 

 somewhat greater than the amplitude of the curve. The image 

 of that portion of the curve which was in front of the condenser 

 was now projected on a screen ; and then a piece of cardboard 

 having a narrow slit cut in it was placed close to the disk with 

 the slit in the direction of one of its radii. On now revolving 

 the disk I reproduced on the screen the vibratory motion of a 

 molecule of air, or of a point on the tympanic membrane, when 

 these are acted on by the joint impulses of the first six harmonic 

 or pendulum-vibrations forming a musical note. On slowly 



