206 ENQUIRY into tHe CAUSE or 
properties of this wonderful fubftance, light, which ani- 
mates all nature in the eyes of man, and perhaps above 
all things difpofes him to acknowledge the Creator’s boun- 
ty. But want of leifure obliges me to quit the fubje&t for 
the prefent. 
I am, dear fir, your affectionate friend, 
And very humble fervant, 
DAVID RITTENHOUSE. 
N° XXV. 
An Enquiry into the Caufe of the Increafe of Bilious and 
Internitting Fevers in Pennfylvania, with Hints for 
preventing them. By BENJAMIN Rusu, M. D. Pro- 
Seffor of Chemiftry in the Univerfity of Pennfylvania. 
Real December FT has been remarked, that Pennfylvania for 
fome years paft has become more fickly than 
formerly. Fevers which a few years ago appeared chiefly 
on the banks of creeks and rivers, and in the neighbour- 
hood of mill-ponds, now appear in parts remote from 
them all, and in the higheft fituations. This change with 
refpe&t to the healthinefs of our country, may be traced 
to the three following caufes. 
1. The eftablifhment and increafe of mill-ponds. There 
are whole counties in Pennfylvania in which intermittents 
were unknown, until the waters in them were dammed, 
for the purpofe of erecting mill-ponds. 
2. The cutting down of wood, under certain circum- 
ftances, tends to render a country fickly. It has been re- 
marked that intermittents on the fhores of the Sufquehan- 
nah have kept an exact pace with the paflages which have 
been opened for the propagation of marfh effluvia, by 
cutting 
