Striking Point of Pianoforte Strings. 649 



violin. The writer has used apparatus of a similar nature, 

 the principle of the arrangement being that a beam of light 

 is set vibrating by the sounding-board or other part of the 

 musical instrument and this beam of light traces a wavy line 

 on a moving photographic plate or film and the result is in 

 the nnture of a time-displacement curve. 



A photograph of the apparatus is shown in PL X. fig. 1. 

 K I} K K , K m are sections of sounding-boards of a pianoforte. 

 In this paper the section K^ only was used. The sections are 

 glued ;md screwed to a strong wooden frame, the construction 

 of a pianoforte being followed as closely as possible, and 

 the whole securely bolted to the main wall of the building. 



The steel string used weighed 0*062 grm. per cm., 

 had a vibrating length of 66 "5 cm., and was tuned to 

 c' 261 vbns./sec. 



The hammer H forms part of a section of a a tnpe check " 

 action, and is caused to strike the string by allowing the 

 weight W to fall on the top of the key. 



The weight falls 2*7 cm. vertically and weighs 128 grm. 



A concave galvanometer mirror M is mounted on a table 

 on the " hole, slot and plane " system as described by 

 Dr. Barton. 



In PI. X. fig. 2, L is a straw forming the connexion between 

 the sounding-board and the table carrying the mirror. The 

 straw hus a small wooden base block, and a needle, driven 

 into the block and into the sounding-board, holds it in its 

 place. Two small aluminium nuts grip the other end of the 

 straw. The mirror turns on a vertical axis passing through 

 the hole and slot. A beam of light from an electric arc 

 passes through a pin-hole (these are not shown in the photo- 

 graph), falls on the mirror M, and after reflexion passes 

 through the shutter S and is brought to a focus upon the 

 cylindrical drum of the phonograph G. The latter is turned 

 to face the mirror when in use. 



The weight and shutter are released simultaneously by 

 pressing the bulb B. The films used were the " Kodak 

 Brownie No. 1 *' ; a strip of the film being fastened round 

 the drum of the phonograph. The mirror and table are 

 carried by an adjustable cross-bar which is not directly 

 connected with the sounding-board except by the straw L. 



Results. 



Plate XI. shows nine photographs taken with the apparatus 

 as described. With the exception of No. 9, the only alteration 

 was in the position of the striking-point. 



From straw to axis of mirror was 0'6 cm. 



