772 PROFESSOR JOHN G. M'KENDMCK 



B. Photographs. 



14. I took numerous photographs, with aid of the microscope and camera, of portions 

 of the surface of the cylinder on which were records of many instruments and of the voice. 

 Specimens of such photographs are shown in figs. 4, 5, 6 (Plate I.). Each figure, from 

 above downwards, represents the ^th of an inch on the surface of the wax magnified four- 

 teen diameters. The grooves seen in each figure are, on the wax cylinder, 200th of an inch 

 apart, and the length of the groove, from above downwards, represents in time the ^th 

 second ; that is to say, when each tracing was recorded, the sapphire point of the 

 recorder travelled over the distance represented in magnified proportions in -g^th part of a 

 second. By counting the number of indentations or marks, which in a photograph have 

 a curious appearance of being in relief, one can at once determine approximately the 

 pitch of the tone, the vibrations of which make the impression. The tones highest in 

 pitch were obtained from the piccolo and the xylophone, as in figs. 7 and 8 (Plate I.). 

 Here the pitch was about 1920 vibrations per second. In fig. 9 we have a picture of the 

 vibrations produced by the tones of the violin, and it will be seen that they vary in 

 character. Sometimes the marks are a little apart and at other times they blend into 

 each other, the mark widening out as the recording point cut into the wax and then 

 contracting as it receded. It is to be borne in mind that even when the glass disk is 

 not vibrating, the recorder ploughs a groove in the cylinder, and when the glass disk 

 vibrates, each vibration cuts deeper into the groove. The figure of the vibrations of the 

 tones of a flute (fig. l) shows moniliform markings, indicating that the disk may not, in 

 some instances, return to its position of rest for a short time. In accordance with the 

 description already given of the mechanism of the recording point, it will be seen that, 

 in the figure of the vibrations of the tones of an organ, the intensity of the tone is so 

 great as to cause after each deeply ploughed groove a rebound lifting the recorder on to 

 the surface of the cylinder, or even off the surface altogether. This is the explanation 

 of the smooth spaces between the ends of individual furrows. This action is also well 

 seen in fig. 10, showing the strong vibrations of a tuning-fork. Here one can distinctly 

 observe the slight groove, made by the very tip of the recorder, between the individual 

 vibrations. 



15. The accuracy of the phonograph is well illustrated by the four records, figs. 11, 

 12, 13, and 14. Here we have four records from four of Koenig's tuning-forks, the 

 vibration numbers of which are 64, 128, 256, and 512. When the records were taken 

 the cylinder of the phonograph was making as nearly as possible two revolutions per 

 second. Photographs were then obtained of portions of the cylinder representing 

 vertically J^th second. It will be noticed that in fig. 1 1 there is one mark or vibration in 

 the ^th second ; in fig. 12 there are two marks (64x2 = 128); in fig. 13 there are four 

 marks (64x4 = 256); and in fig. 14 there are eight marks (64x8 = 512). As the 

 phonograph travels with remarkable uniformity of speed when it is in good working 

 order, we may rely upon it as an instrument for determining pitch, provided the time 



