﻿S&8 Prof . Barton and Mr. Kilby on Simultaneous 



was of the order 0*12 cm. Hence the magnification of the 

 membrane's motion on the negatives was 2667 nearly. 



Thus the ratio of magnifications of motions of mem- 

 brane and string on the originals, or any reproductions 

 of them, is of the order 2667-i-3'86 = 691 nearly. Or, in 

 other words, the membrane's motion is magnified neaily 700 

 times that of the string's motion. 



Results. 



One hundred and forty plates were exposed, and of these 

 sixty-one reproductions are here presented. 



These naturally fall into three series, those taken under 

 the ordinary conditions of shooting, first, with the clamp- 

 mounting of the mirror ; second, with the belly mounting ; 

 third, those taken under the special conditions of shooting 

 to record the initial stages of the motions, the belly mounting 

 being here retained. 



The distances from the bridge at which the strings were 

 excited are stated near each figure as a fraction of the 

 string's length. In these marginal references " plucked " 

 means plucked by the finger-tip ; " plucked by plectrum' 

 refers to excitation by the point of a pencil. " Struck " 

 denotes a blow struck by a lead-pencil padded with two or 

 three thickness of wash-leather ; u struck by wood/' refers 

 to a blow by the naked edge of a hexagonal pencil. 



As to the interpretation of the abscissae and ordinates of 

 the curves on the prints : — 



(1) The beginning of the time is in all cases at the left- 

 hand side. 



(2) The ordinates for the strings' motions are always 

 inverted. 



(3) The ordinates for the membrane's motion are also 

 inverted. 



Clamp Mounting. — The first series of figs. 1-22 of PL XIV. 

 deals with the motions obtained when the mirror axle was 

 supported by a bracket clamped at a corner of the violin. 



Fig. 1 for the G-string bowed at ^ shows a good two-step 

 zigzag for the string as it should do, and also a large and 

 characteristic motion for the air. This motion is much 

 feebler and less marked in the next figure for the same 

 string bowed at I. Fig. 3 shows a large motion of the 

 plucked string, but only a moderate motion for the air by 

 this method of shooting. The air's motion recorded in 



