EFFECT OF TEMPERATURE ON COPPER. 283 
‘same end was attained in the compression tests by the use of an 
ordinary cup bearing. 
The oil used in the majority of the tests was a very heavy 
cylinder oil guaranteed not to “flash” at 700° F., and which proved 
in every way satisfactory. For a few of the tests at the lower 
temperatures the oil was replaced by a mixture of ice and water, 
or ice and salt. The actual range of temperature attained was 
from 25° F. to 535° F. The temperatures with the exception of 
those in the neighbourhood of the freezing point were measured 
by means of a mercurial thermometer, graduated to two degrees 
and reading to 600° F. The readings of this thermometer up to 
410° were compared with those of two mercurial thermometers pro- 
vided with Kew certificates, and it was found to have a small 
negative error in the neighbourhood of 100° diminishing to zero 
at about 300°, and increasing to a small positive error in the 
neighbourhood of 400°—the maximum error being two degrees. 
From 420° to 500° it was compared with a nitrogen thermometer 
reading to 900° F., but not certified. As however the relative 
readings of the two were uniform over this range, there is no 
reason to suspect the presence of any errors, but such as are 
negligible for the purposes of these tests. 
The extensions and compressions in the majority of the tests 
were measured by a special modification of Kennedy’s well known 
lever-extensometer. This instrument is provided with a scale 
reading nominally to -0001 inch, but it was calibrated by com- 
parison with a Brown and Sharpe micrometer calliper, and the 
Scale values so obtained were used in plotting the stress-strain 
curves. In three tests, one in tension and two in compression, 
the strains were measured by means of Marten’s mirror extenso- 
meter reading to 0001 mm. This instrument and its proper 
method of use have already been brought before the Society.’ The 
autographic diagrams were obtained by means of the apparatus 
attached to the Greenwood and Batley testing machine. 
Phage a mm A 
1 See papers read by Prof. Warren, and by Mr. G. H. Knibbs.—Proc. 
Roy. Soc., N. 8. Wales, Vol. xxx1., pp. 89-111. 
