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 water 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 afforded, is to highly heated water, 



