Meteorology-^Chemistry. J79 



The proportion and size of these different constituents vary considerably 

 in different specimens ; but all of them bear a striking resemblance to each 

 other. The specific gravity varies from 3.352 to 4.281. 



Dr Tytler then noticed the different theories that have been proposed 

 to account for the appearance of these aerolites, and shows that none of 

 them are free from objections. He then suggests their terrestrial origin, 

 and that they have been emitted from volcanos upon the surface of the 

 earth, for the following reasons : 



1^;, The stones in their appearance plainly bespeak a volcanic ori- 

 gin, and it is evident they have been subjected to the action of intense 

 heat. 



2<f, Their descent is ascertained to be accompanied with a sulphurous 

 smell, and the emission of fiery sparks, while the stone itself is constantly 

 found hot. 



3rf, Stones of this description have descended in considerable numbers 

 during eruptions of Vesuvius, and at a great distance from the volcano. 



Uh, Stones of the same kind are very frequently found on the sides of 

 Vesuvius. 



6th, These stones distinctly coincide with, or rather their substance 

 is precisely the same, with that of meteoric stones. 



6th, The meteoric phenomena attending the descent of the stones are 

 also volcanic, 



7ih, And lastly, the meteors emitted from the craters of volcanos also 

 upon their explosion eject stones. In proof of these assertions he quotes 

 various recorded facts. 



In connection with the volcanic origin of the stones in question, Dr 

 Tytler refers to the occurrence of a remarkable volcano on Java in No- 

 vember 1822, and thinks it not improbable that they might have been 

 thrown out on that occasion, being projected far beyond the elevation of 

 the atmosphere, and falling to the westward of Java, conformably to the 

 diurnal motion of the earth, the meteor having visibly passed in a direc- 

 tion from south-east to north-west. 



II. CHEMISTKY. 

 14. M. Despretz on the Heat Developed in Combustion.-^Ow the 15th and 

 22d October last, M. Despretz read at the Academy of Sciences a memoir 

 on the heat developed in combustion. By means of a new method of ob- 

 servation he found that hydrogen is the body which, under a given weight, 

 disengages most heat, and that the metals disengage least. The result 

 will be opposite if we refer the results to the same weight of oxygen. It 

 is remarkable that carbon, which in burning does not change the volume, 

 of oxygen gas, produces three-fifths of the heat developed by the metals, 

 (iron, zinc, and tin,) which reduce the oxygen gas to the solid state. 

 Hence it is in the act of combination that we must seek for the principal 

 cause of the developement of heat, and not in the approach of the particles. 

 In his second memoir M. Despretz has shown that the quantity of heat 

 developed by a certain quantity of a body which burns without changing 



