774 PROFESSOR JOHN G. M'KENDRICK 



the drum a. Thus the amount of surface on a, representing one-half second on cylinder 

 6, could always be measured. As a rule, it was found that 3 inches of the drum a 

 represented one-tenth of a second. Occasionally it was one-seventh of a second, but it 

 could be so timed as to represent one-tenth. 



18. In the next place, a light lever of hard wood, braced like the mast of a ship, 

 was fixed firmly into a socket bored into the lead weight, i k, seen in fig. 16, Plate I. 

 This square leaden weight is hinged to the frame carrying the recording and repro- 

 ducing part of the phonograph by the hinge h, a slot is cut in the under surface of 

 the lead weight, as seen in fig. 17, Plate I., and the marker, a n (also mwin fig. 16), 

 moves on an axle delicately pivoted to the sides of the slot. In fig. 16, at the end of m t 

 is seen the wire, w, passing up to the glass disk, d, of the phonograph. It will be seen 

 that the point of m n touches the surface of the wax cylinder, o, o, o, o. The lead 

 weight accurately follows the movements of m n, the marker, and the lever a' records 

 these movements, as seen in fig. 15, on the drum a. The slowness of movement does 

 away with any movement of s, except that which is communicated to it from the lead 

 weight and from the marker, m n, and to prevent all extraneous vibrations the phono- 

 graph was seated on a solid stone pillar erected for a galvanometer. The point of the 

 lever s is the point of a very fine hard needle, and a was covered with very smooth 

 paper, carefully smoked. As the marker of the phonograph is always travelling to the 

 one side so as to describe a spiral groove, that is, towards the observer, when one looks 

 at fig. 15, it is evident that the point of the lever x would soon leave the surface of a. 

 To get rid of this difficulty, the drum a is mounted on a kind of movable table moving 

 in slots, and controlled by the fine screw c (one thousand to the inch thread). And 

 thus it was easy, by a turn of c, to keep the point of x in contact with the surface of a. 

 Finally, the movable table rested on a plate of metal moving vertically in slots by 

 turning the fine screw b, and thus, after a tracing had been taken once round a, it was 

 easy to move a a little up or down without disturbing the lever x (fig. 15). Thus I had 

 three motions of a, vertical, rotatory, and horizontal, and there were two movements 

 of the cylinder of the phonograph b, rotatory and horizontal. Everything was as steady 

 as it could be made, and the apparatus worked almost automatically, the point n (fig. 

 16) slowly crawling over the surface of the wax cylinder o, about 600 times slower than 

 when the record was made on the wax cylinder. 



19. After tracings had been taken, the paper on a was varnished and it was 

 cut into longitudinal strips, each 3 inches in length, and the strips were mounted 

 between two ordinary microscope slides (English make) in the way that slides are 

 prepared for the lantern. Such slips can then be examined by the microscope and the 

 curves may be drawn by Abbe's camera lucicla, or any portion of the tracing may be 

 photographed by a convenient microphotographic apparatus. Thus the size of the curves 

 may be much increased, and so made available for purposes of harmonic analysis. 



20. This apparatus, which was large and clumsy, was discarded for the small 

 and more convenient apparatus, consisting of a train of four sets of wheels and 



