120 OF METEORS. CHAP. 3. 1. 



supposed to happen to phosphorific matter. 

 There are several other appearances which in- 

 cline one to think, that there are combustible 

 gaseous exhalations from the earth, which after- 

 wards ignite. The next question is, if they 

 are only phosphorific, as M. De Luc calls them, 

 what is the principle of their ignition ? They 

 may, perhaps, be ignited, by getting up into a 

 dryer atmosphere. This supposition is agreeable 

 to the known properties of phosphorus, which 

 is preserved in water, but burns if left to dry. 

 It may perhaps be conceived that phosphorous 

 gases may be preserved while passing through 

 a humid atmosphere; but which, when they 

 arrive at a more dry air, spontaneously take 

 fire. The ignition being thus began, it would 

 probably extend down the column of phospho- 

 rific vapour, and give the appearance of a 

 descending luminous ball, just such as we see 

 to be the case : and it might go out when it 

 had descended again so low as to be in an air 

 too humid for combustion. Or its extinction 

 may, in other cases, be caused by the column 

 of vapour being interrupted by wind, or any 

 other cause of dispersion. 



Upon the above supposition, the motion of 

 the falling star would be exactly retrograde to 



