APPENDIX. 2gt 
and Thunder are frequent in the Night, which 
fliOLild therefore at that time arife from an Effer- 
vefcence in the Air 5 which EfTcrvefcence may 
very probably be frequently kindled into Light- 
ening, as the learned Dr. Boerhaave obfcrvcs 
in his excellent and elaborate Ekmenta Che^ 
mi£.^ Vol. I. p. zji. by the Rcfradtions and 
Refle£Hons of the Sun Beams among the 
Clouds. 
ly. That the crooked Dartings of Light- 
ening arc not owing to its following a Train 
of fulphureous Vapours in the Air^ is proba- 
ble hence, viz. that if a large Viol, which 
has all its Air exhaufted, be ftruck on its Side 
with the Palm of the Hand, there will iflue 
thence pale, livid, pointed and crooked Flafli- 
cs, four, five or fix Inches long, which Crook, 
ednefs cannot in this Cafe be attributed to a 
Train of fulphureous Vapours; for the fame 
Event will happen, let the Viol be ftruck ne- 
ver fo often, whether it continues in the fame 
Place or be removed. The Impetus therefore 
of Lightening feems to be given it, at or near 
the firft Explofion of the fulphureous Vapours, 
its Force being more or lefs in Proportion to 
the Qiiantity of thofe Vapours which are at 
once enkindled. 
U 2, 
E X P £ R I- 
