ROCK TEMPERATURES IN VICTORIA. — 313 
due to the depth of the mine. Ground containing such 
minerals will give abnormal temperatures. 
3rd. Very wet ground must be avoided. It will generally 
involve a lower temperature reading than the true one, for 
in the ordinary cases of percolation the water will be prac- 
tically all coming from higher ground. Occasionally the 
water will come from below, but this can nearly always be 
recognised and avoided. , 
4th. Sufficient time must be given to the hole that has 
been drilled for the insertion of the thermometer, in order 
to allow the ground near it to come back after boring to 
the original temperature of the rock. Under the ordinary 
conditions of drilling, about two days seem to be quite suffi- 
cient, the hole being plugged up meanwhile. 
5th. The hole must be deep enough, in order to get rid 
of the disturbance of temperature of the rock at the face. 
Agassiz appears to have used holes 10 feet deep from the 
face; this seems excessive for new faces, and the author has 
ordered “‘ 6-feet ’’ holes as a standard depth; this has gener- 
ally given a distance of 5 feet 6 inches from the thermometer 
coil to the face. : 
The holes under these conditions of determination have 
to be horizontal ones, and the weight-thermometer would 
need to be of a shape fatal to accuracy of work before it 
could be made symmetrical about an horizontal axis, it is, 
therefore, quite inapplicable. The author has used several 
other forms of mercurial thermometers, but finds that an 
ordinary high-class chemical thermometer, having divisions 
to 0:10° Centigrade, can be easily withdrawn from a hole 
and read off, if its bulb has first been wrapped around with 
about three layers of finest flannel, and the thermometer 
supported upon cork mounts then enclosed without pressure 
in an outer and sealed glass tube. The correction under 
these conditions proved to be of no practical moment at all, 
if the instrument be read off promptly, say within 10 seconds 
of the time of its withdrawal. 
The handiest maximum thermometer for this work is un- 
doubtedly an ordinary clinical one, in which the thread of 
mercury is broken by a constriction in the bore, and so 
prevented from returning. With reasonable care there is no 
danger of alteration of reading on withdrawal. Some pat- 
terns of these clinical thermometers can be obtained with an 
open scale, reading from 90° Fahr. up to 115° Fahr. by 
0-05 degrees, and are used by veterinary surgeons. For 
other ranges of temperatures the thermometers must be 
