Geological Societt/. 477 



Results were sought for, by which the magnetic force of bodies, 

 already examined in the condition of magnecrystals, might be com- 

 pared with the whole paramagnetic or diamagnetic force of the same 

 bodies taken in the granular or amorphous state ; but they were not 

 satisfactory. The carbonate of iron gave the most distinct results ; 

 and in its case the change of power by change of temperature was 

 not the same for the two conditions. An examination of the three 

 metals, iron, nickel, and cobalt, at temperatures between 0" and 

 300° F., gave a very interesting result, which the author is not 

 aware has as yet been noticed. As the temperature rises, the force 

 of the nickel diminishes, the force of the iron remains constant, the 

 force of the cobalt increases ; these facts suggest tliat there is a 

 temperature at which the magnetic force is a maximum, and above 

 or below which it diminishes. The order with the three bodies 

 accords perfectly with that in which they lose the chief amount of 

 their magnetic power, for much loss occurs with nickel at the tem- 

 perature of boihng oil, with iron at a duU red heat, and with cobalt 

 at a temperature near that of melting copper. 



GEOLOGICAL SOCIETY. 



[Continued from p. 398.] 



April 23, 1856.— Daniel Sharpe, Esq., President, in the Chair. 



Mr. G. Poulett Scrope, M.P., F.G.S., read a paper " On the 

 Mode of Production of Volcanic Craters, and on the Nature of the 

 Liquidity of Lavas." 



The author referred to the two works published by him thirty 

 years since, namely, ' On Volcanos' in 1824, and ' On the Volcanic 

 Formations of Central France' in 1826 ; being desirous of calling 

 attention to certain theoretical views developed in both, which were 

 either controverted at the time or met by opposite theories, but which 

 he believes the progress of inquiry has since tended to confirm. 



The first point insisted on is the formation of all volcanic cones 

 and craters by the simple process observed in habitually active vol- 

 canos, namely, the eruptive ejection of lavas and fragmentary 

 matter from a volcanic vent ; the accumulation of which around it 

 cannot fail to give rise to the cone-shaped mountain so characteristic 

 of a volcano, and to the crater usually contained in it. The author 

 showed, by the history of Vesuvius, that the cone of that moun- 

 tain has, within the last hundred years, been at least five several 

 times emptied by explosions of a paroxysmal character, and as 

 often refilled by the products of subsequent minor eruptions; 

 while throughout this time the exterior of the cone has been 

 gradually increasing in bulk, and the old crater of Somma as 

 gradually being filled up, by accretions from the volcanic matter 

 ejected beyond the lip of the Vesuvian crater. He refuses to believe 

 that any other process originally formed the outer cone and crater 

 of Somma, than that which he and others have seen to be con- 

 tinually augmenting the inner cone of Vesuvius, and which before 

 his eyes in 1822 scooped out of its heart a crater concentric to that 

 of Somma, three miles in circumference and some 2000 feet in depth. 



