Elastic Constants of Quartz Threads. 



115 



Young's Modulus. 



Method used : — Bar loaded in the middle. 



Two excellent steel knife-edges were fastened rigidly to a 

 block of boxwood which was flat at the bottom, so that when 

 the bottom was horizontal the knife-edges were the same, as 

 tested by a spirit-level. The knife-edges were parallel and 

 4*043 centim. apart ; the thread to be tested was drawn out 

 by the catapult method and measured as to diameter by means 

 of the Zeiss scale in the manner before mentioned. The 

 weight was applied in the form of a rider of round platinum 

 wire, winch was brought to the central point of the thread 

 by a gauge. The deflexion produced was measured by a 

 micrometer-microscope (the one mentioned above as having a 

 practically correct screw). Twelve observations, with the 

 weight alternately on and off, were made on each thread and 

 were always very consistent. Errors due to " loss of time" 

 in the micrometer-screw were of course eliminated. The 

 errors, however, in estimating the deflexion were in any case 

 wholly insignificant compared with the errors of measurement 

 of the thread diameter. No observations of temperature- 

 coefficient were made, as the method was not suitable. A long 

 thread hung down a jacketed tube would be necessary, and in 

 view of our ill success in determining a would be hardly worth 

 experimenting on. The results which I obtained are exhibited 

 in the following table. They were calculated from the 



formula 



F17 



fM = 



12.7T.Z 





L. 



1)1. 



F. 



/. 



Eesulting value 

 of fl. 



Thread. 



Distance 

 apart of 

 knife- 

 edges. 



Radius 

 of thread 

 in centi- 

 metres. 



Weight of 

 Eider in 

 grammes 



multiplied 



Deflexion in 

 centimetres. 



Thick. 

 X. 

 Y. 

 Z. 

 X. 



4043 



•008375 

 •008771 

 •0061015 

 •005593 



•008771 



I 



•3114x979-65 

 •1572x979-65 



•1024x2-54 

 •08623x2-54 

 •10079x2-54 

 •18674x2-54 

 •04316x2-54 



4-1792X10 11 C.a.S. 

 4-1255x10" C.a.S. 

 7-6086 X10' 1 C.a.S. 

 5-8164 Xl0 u C.a.S. 

 4-1628 xl0 u C.a.S. 



Mean value of //, = 51785 x 10 11 . 



12 



