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Geology and Mineralogy. 503 
platinum.—Ann. der Physik und Chemie, No. 10, 1895, pp, 360- 
396. Jr 
9. Absorption of Kathode rays.—The phenomenon of kathode 
rays is receiving much attention from various observers in Ger- 
many and England. The current number of the “ Annalen der Phy- 
sik und Chemie” contains two papers on thissubject. P. Lenarp 
investigates the permeability, so to speak, of many gaseous and 
also solid media to the kathode rays and endeavors to frame a 
law which will express a relation between the absorption power 
and the thickness of the layers. O. LEHMANN criticises the 
results of Pliicker, Hittorf, Goldstein, Crookes, Hertz, E Wiede- 
man and H. Ebert.—Ann. der Physik und Chemie, No. 10, 1895, 
pp. 255-275 and pp. 304-346. J. T. 
If. GroLoGy AND MINERALOGY. 
1. On underground temperatures at great depths; by ALExAN- 
DER AGassiz (from a letter to the editors, dated Calumet, Mich., 
Noy. 14, 1895.)—For several years past I have with the assistance 
of our engineer, Mr. Preston C. F. West, been making rock tem- 
perature observations as we increased the depth at which the 
mining operations of the Calumet and Hecla Mining Co. were 
carried on. We have now attained at our deepest point a 
vertical depth of 4712 feet, and have taken temperatures of the 
rock at 105 feet, at the depth of the level of Lake Superior, 655 
feet, at that of the level of the sea, 1257 feet, at that of the deep- 
est part of Lake Superior, 1663 feet, and at four additional stations 
each respectively 550, 550, 561 and 1256 feet below the preceding 
one, the deepest point at which temperatures have been taken 
being 4580 feet. We propose, when we have reached our final 
depth, 4900 feet, to take an additional rock temperature and to 
then publish in full the details of our observations. 
In the mean time it may be interesting to give the results as 
they stand. The highest rock temperature obtained at the depth 
of 4580 feet was only 79° F., the rock temperature at the depth 
of 105 feet was 59° F. Taking that as the depth unaffected by 
local temperature variations, we have a column of 4475 feet of 
rock with a difference of temperature of 20° F. or an average 
increase of 1° F. for 223-7 feet. This is very different from 
any recorded observations; Lord Kelvin, if I am not mistaken, 
giving as the increase for 1° F., fifty-one (51) feet, while the obser- 
vations based on the temperature observations of the St. Gothard 
Tunnel gave for an increase of L° F., sixty (60) feet. The calcu- 
lations based upon the latter observations gave an approximate 
thickness of the crust of the earth, in one case of about 20 miles, 
the other of 26. Taking our observations, the crust would be 
over 80 miles and the thickness of the crust at the critical tempera- 
ture of water would be over 31 miles, instead of about 7 and 8°5 
miles as by the other and older ratios. With the ratio observed 
here, the temperature at a depth of 19 miles would only be about 
470°, a very different temperature from that obtained by the older 
ratios of over 2000° F. 
