EXPERIMENTS on EVAPORATION. 125 
ling, and no part of the infide fuffered in the leaft, not- 
withftanding that the ftroke, by the prodigious noife which 
accompanied it, {eemed to be very powerful. 
It is remarkable that a perfon was fitting at the time in 
a door on the ground floor, not more than 4 feet from the 
lower end of the copper fpout, who received no injury, 
though he very fenfibly felt the thock. 
From our obfervations on the above cafe, as well as fome 
others that have occurred, we would ftrongly recommend 
to thofe who put up pointed rods, that the lower end be 
funk fufficiently deep to reach moift earth in the dryeft fea- 
fons. And we fubmit it to thofe converfant with electrical 
philofophy, whether, when there are more rods than one 
to a building, it might not conduce much to its fafety to 
form a good communication between the rods, and like- 
wile between them and a copper water fpout; carrying 
an iron or copper rod from the lower end of the {pout a 
fufficient depth into the ground. 
Thinking it poffible that the above may afford fome 
hints for improving the means, now pretty generally in 
ufe, for guarding againft the fatal effets of thunder ftorms, 
we have thought proper to lay it before the Society, and 
fhall be happy if it receives their approbation. 
N°. XVI. 
Experiments and Obfervations on Evaporation in cold Air, 
by GC. Wistar, M.D. 
Read Sept. URING an experiment with a frigorific 
ae mixture, I frequently had occafion to intro- 
duce my hand when it was wet, into a cold veffel, and 
obferved that while it was in this fituation, a fmoke or vi- 
fible vapour arofe from the moifture on it, which ceafed 
when it was withdrawn into warmer air, and returned 
upon my replacing itin the veflel. In 
