150 Observations on the luminous Meteors 



situ, showed the same reluctance to fuse in one instance as in 

 the other. Although the porphyries were fused ultimately, 

 and with effervescence, they required three times the heat 

 which was necessary to melt the basalts. This result is just 

 what might be expected, when we know, by means of this 

 instrument, that hornblende, or augite, is the principal mineral 

 constituent of basalt, because either is so much easier melted 

 than felspar, which latter is the principal mineral substance 

 in the composition of the porphyries. 



Those substances which contain the smallest proportion of 

 silex are the most ductile under heat. We find that horn- 

 blende has a less quantity of silex, by nearly twenty per 

 cent, in its composition, than most of the felspars ; and this 

 is the reason that basalt, which is mainly composed of horn- 

 blende, fuses so much quicker than porphyry. 



Having some modern basaltic lavas by me from Vesuvius, 

 I submitted portions of them to this blow-pipe. I found that 

 some of the basalts from the gravel, and some of those from 

 Scotland, fused as easily as the lava of 1805. 



The blow-pipe would not, perhaps, be worthy of confidence, 

 as a test for making us acquainted with some of the charac- 

 ters of rocks, if the same results were obtained in the trap, 

 the mechanical, and fossiliferous limestone rocks. But dif- 

 ferent results were effected, as specimens of the latter were 

 submitted to its heat. Several varieties of oolite, mountain 

 limestone, calcareous spar, millstone grit, and several siliceous 

 sandstones were tried with the same degree of heat as that 

 which fused the trap, &c; but fusion could not be effected in 

 any of them : the grit and sandstones vitrified only. A speci- 

 men of old red sandstone, from its having felspar in its com- 

 position, was more altered than any of the others ; while, at 

 the same time, a fragment of green porphyry, with the same 

 degree of heat, fused instantly into a dark glass globule. 



Stanway, Jan. 2. 1837. 



Art. IX. Observations on the luminous Meteors commonly 

 termed Shooting Stars. By Jonathan Couch, Esq., F.L.S. 



The meteorological constitution of the atmosphere is, 

 perhaps, less understood than any other department of 

 science ; of which we have a remarkable proof in the insuf- 

 ficient, not to say absurd, explanations that have been 

 hazarded in reference to the phenomena of the luminous 

 meteors commonly termed falling, or shooting, stars, con- 

 cerning which what has been advanced is scarcely more pro- 



