850 Kohlrausch and Loomis—Influence of Temperature 
cope shall be effected by the light transmitted through the body 
of the microscope. So arranged, the apparatus remains in con- 
stant readiness for use, and, as before remarked, requires only 
the labor of taking two microscope readings for each determin- 
ation of level error, dae involving any disturbance of the 
setting of the instrum 
I may add in closing, ha this virtual mirror of constant incli- 
nation to the horizon may easily find other applications,—as for 
instance in determining the horizontal points of a vertical circle 
vile a the object ~ oi the instrument is not so large as to 
eldy and expensive prism. 
ee N. H. Aug. 1, 1870. 
2 
A 
Arr. XXXVIL—IJnfluence of Temperature on the modulus of 
Elasticity of certain Metals; by F. Konn~rauscu, Ph.D., and 
Francis E, Loomis, Ph.D. 
[Communicated in extracts to the Academy of Sciences, Géttingen, May 7, 1870.] 
THE results obtained by Wertheim,* in his investigations re- 
specting the influence of temperature on elasticity, ae thus 
far generally served as a basis for calculation. It will e ob- 
served in comparing these data, that for certain sbokane. espe 
cially for iron, the singular phenomenon manifests itself that 
for different temperatures the variations of the modulus under- 
go achange of sign. From 0° C. to 100° the modulus increases, 
and then from 100° to 200° decreases. ‘This increase is certain- 
ly altogether contrary to what would naturally have been ex- 
ted. Such a maximum, however, is still more remarkable. 
view, sherefora, of the uncertainty of the results of investi- _ 
gations thus far made known, and the importance of an accu- 
rate knowledge of the variations of the modulus of alaaticity 
for different temperatures in many of the finer measurements, 
the ee investigations were undertaken with a view if pos- 
sible of obtaining more reliable results for some of the metals 
of greats pracece) utility. For practical purposes it would 
ce to determine the variations of elasticity within the lm- 
its of the more ontinatily occurring temperatures. This was 
partially accomplished by Kupffer, whose investigations we shall 
refer to hereafter. Nevertheless in consequence of the results 
obtained by Wertheim, it appeared of especial interest to "deter: 
mine again the variations in regard to their uniformity, as we 
as in regard to a change of sign. The observ ar were €X- 
tended therefore to high oe in general from 90° to 
20° C., and in one case very nearly to 0°. Within these limits 
* Pogg. Ann. Erg., Band 2, S. 61; Ann. de Chimie, 3me §., T. 12, p. 443. 
