Mr. Edgeworth’s Experiments t See. 1 3* 
But thefe calculations, and many more of a fimilar nature, 
that are to be met with in beudor’s Architecture Hydraulique, 
and other books, are founded upon a fuppofition that the effect 
of the wind is directly as the fur face upon which it a£ts. If, 
for inftance, its force be eftimated as one upon one fquare ya*rd, 
its force upon two fquare yards fhould be eftimated as two, upon 
three fquare yards as three, &c. ; but in faCt this proportion 
is not to be depended upon, nor muft the refinance of furface3 
be eftimated merely by their extent ; but l'everal other circum- 
ftances muft be taken into confideration. 
No figures can refemble each other more than a parallelo- 
gram and a fquare having the lame fuperficial contents, as 
they are both bounded by four ftraight lines meeting at right 
angles, yet they oppofe different degrees of refiftance to the 
air. 
If two fimilar cards, for inftance, are placed oppolite the 
wind, one upon its end, and the other on its iide, and both 
inclined to the fame angle, the wind will have the greater 
effeCt upon the card that is placed end-ways. 
To determine the difference of refiftance between thefe two 
furfaces, and to afeertain the effect of other figures moving 
through the air, I tried the following experiments. The two 
firft are to be found in Mr. robins’s Treatife upon Gunnery ; 
but I thought it proper to repeat them, that they might be 
more readily compared with others made with the fame appa- 
ratus, elpecially as Mr. robins made ufe of a machine con- 
ftrufted upon a lmaller icale than mine, and turning upon fric- 
tion wheels, which are not proper for machines of this nature, 
nor indeed for any purpofc, where an uniform motion is 
required. 
Vol. LXXIII. T Having 
