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EE INS aT ee eT Pee ee Y 
ee eeT 
ie ie ie os ee 
=e 
eet re re ese ae 
on the Elasticity of certain Metals. 351 
the variations in the — ean be determined from the ob- 
servations with great accuracy. Since they show a remarkable 
uniformity, there can Sse no hesitation in assuming the result- 
ing empirical formula as very nearly accurate, considerably be- 
yond these limits 
It is scarcely necessary to observe that the investigations of 
Wertheim have afforded the most valuable material for a knowl- 
edge of the coefticient of elasticity. His method of observa- 
tion, however, is little adapted to afford = arene of the ques- 
tion here under consideration. For im determined the 
absolute moduli of elasticity by means of the ¢ dilatation of bars 
and wires at different temperatures. The culties besetting 
an absolute determination of the variations of baseline 
amounting in all to only about 14™™ are obvious. 
especially serious for the higher temperatures, since roi imper- 
fect heating apparatus of Wertheim could not be kept at a con- 
_ All ice difficulties disappear, however, and at the same 
e the most accurate method of observation is obtained, by 
ep loying for investigation the torsion elasticity, whose choice 
be to be recommended from the fact that torsion is so 
srenatrally employed in measurements. /If a wire is loaded with 
a weight, and set in vibration about its vertical axis, the recip- 
rocal value of the square of the time of vibration affords a di- 
rect measure for the coefficient of the torsion of the wire. 
ss pop hong of the period of vibration are among _ 
rate known in physics, the variations of e 
nity tot ‘din determined with all the rigor desirable. 
_ L. Apparatus and mode of observation.—The following dis or 
tions were ado ees for the pez be, of ae m 
natural siz 
* Ann. de Chimie, 3me §., T. ee p- 400 and 401. 
