Sti'ess and Strain on the Properties of Matter. 



95 



tudinal vibrations by rubbing ifc as lightly as possible with a resined 

 glove ; a monochord was tuned in unison with the wire, and the pitch 

 of the former then determined by means of the syren. In this way 

 copper, platinum, silver, and platinum-silver were examined, each with 

 two different lengths, one length being about half that of the other. 

 In all cases the shorter length gave a greater number of vibrations in 

 proportion to the inverse of the length than the longer one. The 

 average extent of the deviation is exhibited in Experiment V. 



Experiment V.— -Platinum Wire. 



Length of the wire 

 examined in 

 centimetres, I. 



Number of vibrations 

 per second, n. 



I x n. 



967 4 

 495 -7 



146-47 

 186-90 



141,700 

 142,230 



Here in the case of the shorter length the product I X n is about 

 0"4 per cent, higher than the same product for the longer length. As 

 much greater accuracy than this was to be aimed at for the purpose 

 in view, several days were spent in endeavouring to ascertain what 

 flaws there might be in this mode of experimenting. In the first 

 place the permanent loads placed on the scale-pan were gradually 

 increased in amount, and as the wires were hard drawn, this could be 

 done to a considerable extent without causing any sensible permanent 

 elongation. Evidently, however, the source of error was not to be 

 detected in this way, for though a slight change in the pitch of the 

 note could be detected when the note was reduced below a certain 

 comparatively small amount, yet after this amount of stress had been 

 exceeded, no further addition of load seemed to produce any appre- 

 ciable effect. Secondly, the clamp and vice were shifted and more 

 firmly secured, but still with no good result. 



After this it was decided to place the wire vertically, and as the 

 room was very lofty a considerable length could be tested in this new 

 position. The rest of the arrangement was the same as before, 

 except that now the pulley was dispensed with and the wire was 

 clamped at its upper extremity to a very massive iron plate, and 

 hung freely down through the jaws of the vice before clamping with 

 the latter. The following table gives the mean values of the products 

 Ixn for the different wires examined in vertical and horizontal 

 positions, where I and n have the same signification as before : — 



