[ * 7 ° ] 
than downwards ? but is not this owing to that por- 
tion of the air, which, receiving the heat, and being 
thereby dilated, becomes fpecifically lighter than the 
reft, and therefore rifes in the colder and more con- 
denfed atmofphere ? 6. Suppofe attraction to take 
place, fhould not thofe vapours, by that law, aflume 
a globular form, and not, like a train, contract in 
breadth, and extend in length ? 7. What is to fet 
this train on fire ; fince a ferment, according to the 
chemifis, implies a mixture of heterogeneous parts, 
contrary to the doctor’s hypothecs ? 8. How comes 
this train to be drawn out in fo ibreight a line, and 
of fo equal a breadth, infomuch that, in the path of 
the late meteor, for about 400 miles, there was no 
fenfible deviation, nor any change in the magnitude of 
the luminous appearance, but what might be account- 
ed for from its greater or lefs diftance from the ob- 
ferver, or its being feen through a clearer or an ob- 
fcurer atmofphere ? 
Some have been of opinion, that thefe fiery 
meteors are only a kind of lightning, at greater 
heights .than common ; forming their notion upon 
the velocity of thofe balls of fire, and upon the 
found accompanying them, fo much refembling that 
of thunder. But this bypot hejis having gained no cre- 
dit, I need not employ time in refuting it; and the 
lefs now, as the nature of lightning is fo much better 
underftood than when this theory was firft publhhed. 
I (hall only obferve, that before the matter of light- 
ning was difcovered to be of the eleCtrical kind, it was 
natural to luppole it to be formed of the fulphureous 
vapours arifing from the earth ; and if the earth was 
found proper for producing fuch exhalations, of 
courfe 
