Chemistry and Physies. 319 
33 tons per square inch, and it would rupture if made of any 
material excepting the finest: stee 
The stresses produced by harmonic howianae of high orders 
are next considered. his is in effect case of a series of 
parallel mountains and valleys, corrugati 4 a mean level surface 
with an infinite series of parallel ridges and furrows. 
It is found that the stress-difference depends only on the depth 
elow the mean surface, and is independent of the position of the 
point considered with regard to ridge and furrow. 
umerical calculation shows that if we take a series of moun- 
tains, whose crests are 4000 meters, or about 13000 feet, above the 
intermediate valley bottoms, formed of rock of —— gravity 2°8, 
then the maximum stress-difference is 2°6 ton S per square inch 
(about the tenacity of cast tin); also if the mountain chains are 
314 miles apart, the maximum stress-difference is reached at 50 
miles below the mean surfac 
The solution ene that the atrese-diserance I is nit at the sur- 
t 
Square inch. This maximum is reached in the case of the 4th 
harmonic at 1150 miles, and for the 12th at 350 miles, from the 
ea hig agen ace 
“P our tons per squar BE is figs crushing stress-difference of 
the average granite, aad accordingly it is concluded that at 1000 
miles from the earth’s s urface the materials of the earth must be 
has not the regular wavy character of the zonal harmonics, but 
miles of an equatorial elevation with the rest of the spheroid 
rom this we may draw the conclusion, that either the materials 
of the earth have about the strength of granite at 1000 miles from 
mai surface, or they have a much greater strength nearer to the 
Surface, 
This 5 pak tay must be regarded as confirmatory 0 f Sir 
William Thomson’s view, that the earth is solid nearly Se 
its whole emt “According to this view, the lava which issues 
