136 Stevenson Macadam on a new Theory of the 



Before proceeding further, I shall here make reference to 

 an experiment, as the results which it gives appear to illus- 

 trate v^^hat occurs in volcanic phenomena. 



If a shallow vessel of copper be raised to a temperature of 

 about 400° Fahr., and some drops of nitric acid be projected 

 into it, the nitric acid. (like water placed in the same circum- 

 stances) instantly assumes the spheroidal condition, and rolls 

 about the capsule without any visible chemical action upon 

 it. During the time that the nitric acid is in the spheroidal 

 state, there seems to be a complete cessation of that violent 

 chemical action which characterises the meeting of nitric 

 acid and copper at ordinary temperatures. The duration of 

 the spheroid of nitric acid depends on two circumstances : 

 first, that the heated vessel be directly kept at the required 

 temperature by lamp or otherwise ; and, secondly, that there 

 be a moderate quantity of liquid. For, should the copper 

 vessel be reduced in temperature, either directly, by with- 

 drawing the source of heat, or indirectly, by adding more 

 liquid than the heated vessel can possibly keep in the sphe- 

 roidal state, the nitric acid will wet the surface of the cop- 

 per, violent chemical action will be the consequence, and 

 volumes of nitric oxide gas be given oif. From the above 

 experiment it would appear that — 



1st. There is no chemical action between bodies in the 

 spheroidal state and the hot surfaces over which they are 

 placed. 



2d. That chemical action instantly takes place when the 

 vessel is directly reduced in temperature, or an overplus of 

 liquid added ; in other words, when physical contact is deter- 

 mined between the two bodies. 



In applying the preceding experimental results to volcanic 

 phenomena, I assume, that there exist contiguous to the vol- 

 canoes of our globe (either formed or in the act of formation) 

 basin-shaped cavities, more or less deeply seated, the under 

 part of which is composed of metallic bodies at a high 

 temperature. Water, either from lakes, &c., at the surface, 

 or from subterranean reservoirs, finds access to one of these 

 cavities. The first portion which descends instantly assumes 

 the spheroidal condition, — more water enters, and still it is 



