550 Mr. G. A. Shakespear on an Interference-Method for 



will be unnecessary to give the actual modulus in each case, 

 but the figures denoting the extension or contraction in half 

 wave-lengths of sodium light will be quoted where necessary. 

 The length of wire used is about 28 cm. (28*15 to 28*30 for 

 different specimens), diameter about *075 cm. (*0690 to '0810). 

 It must be understood that the weight applied in all cases is 

 the same. 



In all cases the effect of putting on and removing the 

 weight, and of raising the temperature and letting it fall 

 again, has been to increase the modulus, i. e., the observed 

 extension is always greater at the beginning of operations 

 on any specimen than it is at the end. As examples : a 

 specimen of copper at the beginning showed an extension of 

 317 bands, whereas at the end of the series of observations 

 the elongation for the same load had settled down to be 

 constantly only 279 — an increase of about 12 per cent, in the 

 modulus. Similar figures for a specimen of soft iron are 

 178*6 and 175*9, say an increase of 1*5 per cent. A specimen 

 of silver-steel gave 149*1, falling to 143*7, or an increase of 

 3*6 per cent. A specimen of brass gave 315*3 to 293*7, or 

 an increase of 6*8 per cent. 



In all cases the change of modulus produced by change of 

 temperature from 13° to 100° showed much variation at 

 first, the effect of the first heating being that the modulus 

 was greater at the higher temperature than at the lower, but 

 after this an increase of temperature decreased the modulus. 



The following are some characteristic figures for a specimen 

 of copper : — 







Percentage 







decrease 



Temp. 13°. 



100° C. 



of modulus. 



.of bands: 317*0 



303*0 fist heati 



Qg) —4*4 



291*8 



298*5 (2nd „ 



) +2*3 



287*5 



296*4 (3rd „ 



) +3-1 



283*0 



293*7 (4th „ 



) +3*8 



279*2 



289*4 (5th „ 



) +3*7 



278*0 



287*5 (6th „ 



) +3*4 



278*5 



289-0 (7th „ 



) +3*8 



279*0 



289*0 (8th „ 



) +3*6 



279*0 



289*0 (9th „ 



) +3*6 



279*0 on finally cooling. 



These figures show a gradual settling down to a steady 

 state. 



