^6,2 Olservations on Volcanoes and thiir Lava, 



pious evolution of gas through the whole length of the tube. 

 The wires used in this were iron, and the red and blaclf 

 oxides were formed in considerable quantity. 



Seeing the quaniity of gas evolved with a given power 15 

 in proportion to the quantivv of surface of the wires oppo- 

 sed, many contrivances might be used to increase the effect 

 to a considerable degree. If thin plates of metal were used 

 instead of wires, a greater surface would be opposed, and in 

 all probability the effect would be increased. Several wires 

 or plates might be arranged in the same tube, and alternately 

 connected with the ends of the trough ; or, if wire cloth w&% 

 xiscd instead of plates, probably the effect would be still 

 further increased. 



I am, sir, your obedient humble servant, 



William Wilson. 



XL. Neiv Olservations on Volcanoes and their Lava. By 

 G. A. Deluc*. 



V OLCANOES have been so numerous on the surface of 

 our continents, when they were under the waters of the 

 antient sea; and as this class of mountains, raised by sub- 

 terranean fires, manifest themselves still on the shores of 

 the present sea, and in the middle of its waters, it is of 

 importance to geology and the philosophy of the earth to 

 obtain as just ideas of tliem as possible. 



I have attended a g>-eat deal to this subject from mv own 

 observations ; and 1 have shown, at different times, the 

 errors into \yhich several geologists and naturalists, in 

 treating ot it, have tallcn. 



This class of mountains, in particular, requires that we 

 should see thei-n, that we should behold them during their 

 eruptions, that we should have traced the progress of their 

 lava, and have observed closely their explosions ; that we 

 should have made a numerous collection of the matters 

 which thcv throw up under their different circumstances, 

 that we might afterwards be able to study them in the ca- 

 binet, and to judge of their composition according to the 

 phtcnomena which have been observetl on the spot. 



This study is highly necessary when we apply to geology 

 and the philosophy of the earth, in order tliat we may avoid 

 fallino- into those mistakes which make us ascribe to sub- 

 terranean fire? what does not belong to them, or which 

 It^ads us to refuse them what really belongs to them. 



• From Jeurnal dc Mines, I'hermidor, An. xii. No, 95. 



We 



