a 
supposed by many that the solid crust beneath our feet is not more 
than forty or fifty miles thick. It has however been assumed that the 
increasing pressure at increasing depths does not alter either the 
conducting power of materials, or the temperature at which they 
melt. This no doubt is to a certain extent incorrect, and it is highly 
probable that the conducting power of the different strata increases 
considerably with the depth, the materials becoming more compact 
under augmented pressure. It is not improbable also that pressure 
may raise the temperature of fluidity. In either case the solid crust 
of the globe would be thicker than it had been supposed to be on 
the assumed data. With the view of throwing light upon this 
question so interesting to all geologists, Mr. Hopkins undertook, 
with the assistance of Mr. Fairbairn and Mr. Joule, to subject 
various substances under different temperatures to enormous pres- 
sure. Considerable time was required, even with Mr. Fairbairn’s 
unlimited mechanical means, to construct the necessary apparatus ; 
however, recently it has been completed, and in the few substances 
examined it has been found that the temperature of fusion has 
increased with the pressure : in the case of wax, by a pressure of 
13,000 pounds to the square inch, the fusing-point was raised 30°. 
Whatever may be the influence of these experiments as affecting the 
great questions of Terrestrial Physics, we may predict with certainty 
that data will be obtained most valuable in philosophical research. 
Mr. Joule, I find, has been actively engaged, in conjunction with 
Professor Thomson, in his experiments on the thermal effects of 
fluids in motion, and has determined with considerable accuracy, 
operating on a great scale, the depression of temperature when com- 
pressed air escapes into the atmosphere through a porous plug. The 
laws of the phenomena as to the temperature and pressure of the 
confined gas, will also soon be determined. 
Carbonic acid gas has been found to give a depression of four and 
a half times as great as atmospheric air, while it passes through 
the porous plug with greater facility than atmospheric air ; equal 
volumes requiring pressures of 1 and T05 respectively in order to 
be transmitted in equal times. Certain heating effects of air rushing 
through a single orifice have been observed, which will probably 
lead to a further development of the mechanical theory of the tem- 
perature of elastic fluids in rapid motion. 
The examination of the sedimentary deposits in the Nile valley, 
mentioned at the last Anniversary, is still going on. Mr. Horner 
states, that by the munificent aid of His Highness Abbas Pacha, the 
Viceroy of Egypt, a series of operations have been carried on at 
Heliopolis, and at another station thirteen miles above Cairo, which 
have led to interesting results. A pit has been sunk to the depth of 
24 feet below the pedestal of the colossal statue of Ramses the 
Second, who reigned, according to the chronology of Bunsen, about 
1400 years before Christ, and borings have been continued by which 
cylinders of soil have been extracted at an additional depth of 48 
feet. A series of thirty-two pits has been sunk across the valley in 
a line between the Libyan and Arabian deserts, occupying a line of 
