8S On the Origin of Meteoric Stones. 



of a German vm\e (4§ English), sinks to 14 inches, the air has 

 there only half the specific gravity as at the leveJ of the sea. 

 Now, if it be assumed that the density of the air decreases in geo- 

 metrical progression^ it may easily be calculated that, at the height 

 of 10 German miles, it will be a thousand times, and at 20 Ger- 

 man miles more than a million times, rarer than at the earth''s 

 surface. If, therefore, a cubic rood of ah* weighs 148 lb. at the 

 sorface, at a height of 10 miles (47 English) about 1000 cubic 

 roods, and at a height of ^ miles (93 English) 1,000,000 cubic 

 roods will have an equal weight. These are truly large num- 

 bers; we will, however, make them still larger. Our hypothesis 

 authorised us indeed to assume that the atmosphere, at such 

 heights, consists almost entirely of such vapours; we will not, 

 however, take advantage of this, but suppose that it there con- 

 tains only a small proportion of foreign gases, for example, a 

 promUle^ — then a thousand million cubic roods, only about the 

 eighth part of a cubic German mile (4| English), at a height of 

 20 miles (93 English), would contain 14S lb. «f this foreign mat- 

 ter. This space, brought into a spherical form, would have a 

 diameter of 1240 roods, but, as seen from the earth, would only 

 appear under an angle of 3^°, and this space would afford matter 

 sufficient for a meteoric stone of 148 lb. Even a space a hundred 

 times larger, which would contain materials for a meteoric stone 

 of 14,800 lb. would, at the height of 20 German miles, as seen 

 from the earth, only appear under an angle of scrmewhat more 

 than 16°. This method of calculation gives some sort of concep- 

 tion of the minuteness of such spaces, compared with the im- 

 measurable extent of the atmosphere in these regions. 



It is also easy to conceive that even a momentary annihila- 

 tion of such a body of air, could scarcely put the atmosphere 

 into agitation. It would, indeed, occasion violent commotions 

 in the upper regions, but, on account of the much greater 

 rarity of the air, it is not very probable that any movement could 

 be produced thereby in the lower regions of the atmosphere. 



But how, and by what agents, are such vapours induced to 

 return again to the sohd form ? Since electricity plays such an 

 important part in the atmosphere, and its influence in all me- 

 teoric phenomena is either recognised, or, with probability, as- 

 sumed by philosophers ; it is natural to have recourse here, in 

 the first instance, to this great and wonderful agent. It may, 



