248 W. Hopkins on Changes of Climate. 
The filtrate from the double salts of Platinum, etc., precipita- 
ted by ammonia gave 0-0432 grms. of sesquioxyd of iron = 
6:66 p. c. of iron. The composition of this native Platinum is 
therefore ve 
Platinum, (with palladium,) = 90-24 
Iridium, (with rhodium, ) = 242 
Tron, i : : = 666 
Sisserskite, ee 6S 
160-00 
Arr. XXX.—On the Causes which may have produced Chan- 
ges in the Earth’s Superficial Temperature; by W. Hopxiss, 
Esq., M.A., F.R.S., Pres. G.S., and Pres. Cambridge Phil. Soc. 
—With a Map. 
(Continued from p. 86.) 
1. On the Height of the Snow-line and Descent of Glaciers be- 
low it at the present time. 
20. Knowing the mean annual temperature at any place on 
the earth’s surface, we can calculate for that place the height at 
which the mean annual temperature of the atmosphere will be 
that of freezing, provided we know the rate at which the mean 
temperature decreases, in ascending from+the lower into higher 
regions of the atmosphere. This rate has been determined wit 
sufficient accuracy for our purpose. It is necessary to make @ 
distinction between those observations which have been made 10 
balloons or on the sides of comparatively steep mountains, and 
those which have been made on extensive elevated table-lands 
the results in the two cases being very different. Of the BIS 
class, Humboldt has given us* the results of nine cases, 10 whieh 
the observations were made at different heights, varying from 
about 5,000 to 18,000 feet. The mean of the results gives 191-4 
metres, or about 638 feet for 1° Cent., which is equivalent to 
feet for 1° Fahr. In Gay-Lussac’s balloon ascent, the obser 
tions gave 193 metres for 1° C., up to the height of about 12,000 
eet. At greater heights the decrease of temperature bien ate 
what more rapid, and was at the rate of 1° for 187 metres for ths 
whole height ascended, which amounted to upwards ol 4%)" 
feet. We may adopt, without risk of material error, 190 metres 
for 1° C., or 350 feet for 1° F. In some particular cases, how" 
ever, 320 feet would probably be nearer the truth. _ hich 
Humboldt has also made some valuable observations, W)" 
show the effect of extensive high table-lands in raising the 3 
perature above that which would be given by calculations 18°” 
Ear” 
ii AMMEN eR 
F 4 cut te ieee 
* Recueils Astronomiques of his Travels in S. America, vol. i, p. 129. 
, 
