﻿886 Prof. Barton and Mr. Kilby on Simultaneous 



simultaneous displacement-time records of the vibration. 

 The string's motion appears in the positive print black on a 

 light ground and the air's motion white on a dark ground. 



The place selected as most suitable to give the motion of 

 the air was the lower circular part of the right-hand sound- 

 hole (d t fig, 2). On this accordingly the very thin 

 membrane was placed. But in a preliminary trial it failed 

 to give sufficient motion when the other portion of the hole 

 was left open. The other part was therefore closed by a 

 covering of stiff white paper stuck on (see pp, fig* 2). 

 This sufficiently intensified the motion at the lower end to 

 make it recordable by the membrane and connected mirror. 

 The connector consisted of a strip of aluminium foil of 

 slightly curved cross-section to give stiffness. Its ends 

 were attached to the membrane and mirror by little pieces 

 of animal membrane and shellac* See PL X1IL figi 3, in 

 which d and d' show the normal and displaced positions of 

 the membrane, s the connecting stalk, and n and n! the 

 normals to the mirror m at rest and displaced. The mirror 

 carried a fixed axle consisting of a needle fastened on behind 

 it with a strip of aluminium and shellac. This axle rested 

 in two V-pieces of aluminium and was held down by india- 

 rubber bands. 



Clamp Mounting, — In the first series of experiments, these 

 axle supports were carried on an adjustable bracket clamped 

 on to an outer corner of the violin, as shown in figs* o 

 and 4, pi. vii., of a previous paper (Phil. Mag. Sept. lylO). 

 This clamp mounting applies to figs. 1-22 of PL XIV. of the 

 present paper. But it was felt that this mounting would 

 detect any slight motion of the belly that occurred as well 

 as that of the membrane relative to the belly. 



Belly Mounting. — In order to obtain separate information 

 as to the motions of the membrane relative to the belly in 

 its immediate vicinity, a second mode of mounting was 

 accordingly adopted. This is shown by figs. 2 and 4, from 

 which it may be seen that tiny aluminium brackets support 

 the axle and rest on little packing-blocks of wood on the 

 belly, the whole being fastened by shellac. 



This belly mounting was used in obtaining figs. 23-33 of 

 of PL XIV. and for all the figs. 34-61 of PL XV. 



Initial Motions. — Usually the plates were shot in the rails 

 by one operator after he had heard the sound properly 

 elicited by the other. The plate thus passed rapidly by the 

 opening in the partition very shortly after the commence- 

 ment of the sound and so showed the character of the 

 motions when just established. The elastic threads were 



