for determining Young's Modulus for Thin Wires. 261 



scale-pan to pass downwards along the axis of the screw. 

 The gauge was fixed rigidly in the iron frame bv metal 

 straps, and was placed obliquely to save space. 



The end surface of the screw of the gauge was polished in 

 order to give a reflexion of the hook with which it had to be 

 brought into contact, and thus enable the point of contact to 

 be determined with greater accuracy. A small magnifying- 

 glass was used to increase still further the accuracy of the 



The depression due to the load was determined both while 

 the load was being increased and while it was being 

 diminished. The zeros at no load were taken before and 

 after the loading, and the mean taken if they were in close 

 agreement. If not, the observations were rejected. 



Equation (2) is obtained on the assumption that the 

 supports of the wire are rigid, and in some of the earlier 

 experiments this was tested by placing a second wire in the 

 clamps alongside the wire experimented on, loading it lightly, 

 and observing whether on loading the experimental wire 

 above the limit to which it was proposed to go in the actual 

 experiment, any depression of the subsidiary wire was 

 produced. This was found not to be the case. 



The temperature throughout was that of the air of the 

 room (16° C.). It was not found necessary to take any 

 special precautions to maintain the apparatus at constant 

 temperature. So long as the wire was not touched during 

 an experiment, it came back at the end to the same position, 

 showing that its temperature had remained sufficiently 

 constant. 



The following tables give the measurements made on a few 

 wires, and show the degree of accuracy which can be readily 

 obtained with the apparatus. 



Iron wire, No. 34 S.TY.G. /= 24*05 cms., mean diameter 

 •0230 cm. .*. area a of cross-section ='000415 sq. cm., 



and 9 — =3-28 X 10 1 ©. 

 a 



Initial 

 stretching 



force 

 in dynes. 



M. 



gr. 



y 



mean, 

 cms. 



M 



y ' 



f. 



M\ M 



ih ~ y 



y x *-y*. 



M,_M 



y\ y 



6. 



dynes/sq.ciu. 



>~ot 

 recorded. 



15-50 

 25-50 

 35*50 



•2461 

 •3759 

 •4845 



62-98 



G7-S4 

 73-27 



0605 



1413 

 2347 



486 

 10-29 



•0808 

 1742 



602 



59-1 



1-97x10'- 

 1-94 xW 2 



Mean e = 195xl0 l - 



