66 
lower rocks be twice as great as that of the strata in which 
the observations were made, correcting our former estimate, we 
should probably have to descend 80 or 100 miles, instead. of 
40, to reach a temperature of 3,000°, besides the further 
increase due to the influence of pressure on the fusing point. 
On entirely independent data, Mr. Hopkins has been led to 
conclude that the minimum thickness of the crust does not fall 
short of 800 miles, in which case the superficial temperature 
of the crust would have to be accounted for from some other 
cause than an internal fluid nucleus. 
A Paper was read by J. C. Dyer, Esq., Vice-President, 
entitled “ Brief Notes on the Nature and Action of Steam 
in relation to Boiler Explosions.” 
He stated that several essays had lately appeared on 
boiler explosions, wherein discordant theories and opinions 
are offered on the action of steam in some anomalous 
cases of explosion, and which may justify the bringing 
before the Society a few established facts and prin- 
ciples relating to the subject, in the hope of arriving at more 
settled views concerning causes and effects in such cases than 
appear to prevail at present among our most distinguished 
engineers. The Author objected to the appeals made to Dr. 
Dalton’s theory of atoms for explaining the nature of steam as 
an elastic force mechanically employed, since the law of 
definite proportions of Dalton had no reference to elastic 
vapours except as to the constituents of the liquors whence 
they arise. He then cited the fact that water, like steam, is 
an elastic body, and the pressure would therefore be of the 
same nature and force above and below the w T ater line in a 
boiler ; but that explosions from fractures above or below that 
line would have different effects, owing to the amount of 
expansion of water and steam being so widely different when 
issuing from similar apertures and under the same pressure. 
Many obscure cases of explosion would be explained by the 
more or less rapid generation of steam issuing under those 
circumstances, as set forth in the Paper. That free space , 
when suddenly and amply aft’orded, is to highly heated water, 
