290 APPENDIX. 
calculated the Velocity with which Air rufli- 
cs into an exhaufted Receiver, when driven 
by the whole Preflure of the Atmofphere, to 
be at the rate of one thoufand three hundred 
and five Feet in a Second of time, Lowthorp*s 
Abridgment., Philof, Tranf, Vol. I. p. 6, A 
Velocity fomething greater than that of Sounds, 
which is according to Mr. Derham at the rate 
of twelve hundred and eighty Feet in a fe- 
cond, or a Mile in 4-T8^h Seconds ; no won- 
der then that fuch violent Commotions fhould 
produceWhirl winds, Hurricanes and Thunder- 
Showers, erpecially in the warmer Climates, 
Vv^here both the fulphureous and watry Va- 
pours, being raifed much higher and in great- 
er Plenty, caufe more violent Effefts. Thefe 
Thunderings are alfo obferved to be frequent 
at the End of long Frofis, efpecially far North^ 
and after long Drought, the fulphureous Va- 
pours then arifing plentifully out of the 
Earth. 
14. If the firft enkindling of Lightening 
were from burning Focus's of the Sun's Rays 
only, then there could be no Thunder Storms 
in the Night time, when the Sun was fer, 
but only in the Day time, when it is above the 
Horizon j yet it is well known that Lightening 
and 
