32 INPhUENCE or LIGHT ON THE PROPAGATION OF SOUN». 



ten feet long, and eight inches wide. These two instru- 

 ments having bten tuned to the Paris dia|)ason, on that 

 string of one of the violins which is called the second, be- 

 cause it is the second in the neck, I placed a bit of paper, 

 intended to serve as an index in the course of my experi- 

 ments. 



As it was necessary to be able to bring these violins 

 nearer together, or place them farther asunder, and for 

 their movenacnt to be marked on the plank, that served as 

 the base of the apparatus, I arranged them so that one 

 ifehould be fixed, while the other was movable. The fixed 

 ■was that which had the paper on its second string, and a 

 line corresponding to this string was traced on the plank. 

 The other was movable by means of a very simple contri- 

 vance. A little wooden table was held on the plank by 

 means of two grooves; the violin was placed on this so that 

 it could not be shaken ; and by means of a screw in the end 

 of the plank I could slide this table with the violin on it 

 backward or forward. An opening in the table parallel 

 with the second string enabled me to mark on the plank 

 the changes of place in my experiments, which I conducted 

 as follows. 

 Iss application. With the forefinger, the other fingers resting on the neck 

 of the instruments, I pressed the second string till it touched 

 the third, and then let it go instantaneously. This finger- 

 ing, which was done at a place marked on the table, an4 

 was always uniform, produced an oscillatory motion, 

 •which was heard on the conesponding string of the other 

 violin. The little bit of paper pointed out to me at a dis- 

 tance the vibration of this string, as I separated the two 

 violins till the agitation of the paper became almost null, 

 »nd at length ceased. This point was that of the limit of 

 the vibration. 1 marked it on the table that served to sup- 

 port the apparatus, and numbered it 100. The space be- 

 tween the two strings, which were parallel to each other, I 

 then divided into 100 equal parts; and these hundredths 

 were divided into tenths each at the extremity of the table, 

 that I might have thousandth parts in my scale. This first 

 experiment, which was to furnish me a standard of compa- 

 rison both for the scale of my apparatus, and for the diifer- 



ences 



