102 



Mr. H. Tomlinson, The Influence of 



statical method is decidedly less than when rest has been allowed after 

 the permanent extension, The effect of rest in increasing the elasticity 

 appeared to be less the less the temporary load used in testing the 

 elasticity, and it seemed of some interest to ascertain in the first place 

 the effect of permanent extension on the velocity of sound, and in the 

 second whether rest would, appreciably alter the velocity. The follow- 

 ing experiment was therefore tried. 



Experiment IX. 



A well-annealed iron wire was stretched sufficiently by a temporary 

 load to give a clear note when rubbed longitudinally. The pitch of 

 the note was then taken on a monochord, and again after the wire had 

 suffered more and more permanent extension, the same temporary load 

 being used throughout, and the wire being shortened to its original 

 length after each permanent extension. 



Percentage permanent increase 

 of length. 



Length in centimetres of the 

 wire of the monochord when 

 the latter gave the same 

 note as the longitudinally 

 rubbed wire. 





o-oo 



29-34 





1 82 



29-34 





4-00 



29-34 





6-36 



29-34 





9-10 



29 -34 





13-64 



29-34 





17 00 



29-34 



It will be seen from the above that the pitch of the note remained, 

 as far as could be judged, absolutely unaltered by the permanent 

 extension. After one hour's rest, however, it seemed to be appreci- 

 ably sharper, the frequency as determined by the syren being 458*5 

 as against 458'1, the frequency before stretching and before rest, 

 though after recent permanent extension. It would thus appear that 

 rest after permanent extension does very slightly increase the velocity 

 ot sound in the case of iron. 



The permanent increase of velocity of sound can, however, be 

 almost, if not entirely, accounted for by the diminution of density. 

 The latter amounted altogether to 0*17 per cent., and this diminution 

 would cause an increase in the velocity of sound of 0*085 per cent., 

 whereas the actual increase observed was only 0*087 per cent. We 

 must therefore conclude that the elasticity was not appreciably 

 affected permanently by the permanent extension, though rest did 



