N° XXXVIL. 
A Letter from Dr. BENJAMIN FRANKLIN, to Mr. At— 
puonsus le Roy, Member of feveral Academies, at 
Paris. Containing Jundry Maritime Obfervations. 
sich At Sea, on-board the London Packet; Capt. Truxton, Auguft 1785. 
Read Dec. OUR learned writings on the navigation of 
a cheer the antients, which contain a great deal of 
curious information; and your very ingenious contrivances 
for improving the modern fails (voz/ure) of which I faw 
with great pleafure a fuccefsful'trial'on the river Seine, have 
induced. me to fubmit to your confideration and judgment, 
fome thoughts I have had on the latter fubject. 
Thofe mathematicians who have endeavoured to im-- 
prove the {wiftnefs of veffels, by calculating to find the 
form of leaft refiftance, feem to have confidered a fhip 
as a body moving through one fluid only, the water; and 
to have given little attention to the circumftance of her 
moving through anotiier fluid, the air. It is true that 
when a veflel fails right before the wind, this circumftance 
is of no importance, becaufe the wind goes with her; but 
in every deviation from that courfe, the refiftance of the 
air is fomething, and becomes greater in proportion as 
that deviation increafes. I wave at prefent the confidera- 
tion of thofe different degrees of refiftance given by the 
air to that part of the hull which is above water, and con- 
fine myfelf to that given to the fails; for their motion 
through the air is refifted by the air, as the motion of the 
hull through the water is refifted by the water, though 
with lefs force as the air is a lighter fluid. And to fim- 
plify the difcuffion as much as poflible, I would ftate one 
fituation only, to wit, that of the wind upon the beam, 
the fhip’s courfe being dire&tly acrofs the wind; and I would 
fuppofe 
