3*>7 
I 3§ 0 .] Flighty Aspiration a. 
the results discovered, viz., that propelled against still air, 
at an angle of 15 0 , and at the rate of 25 miles an hour, a 
square foot of stiff plane surface — in this case it was steel 
plate — w ill support a weight of ik lbs., whilst the resistance 
to its forward motion is only 5J ounces ; so that it requires 
but little more than 5J ounces to propel it. 
I must say that if we apply this calculation the result 
of accurate experiment — to Mr. Linfield’s arrangement 01 
area, we do so to its great disadvantage, because he never 
contemplated advancing against the air at such an angle as 
15 0 ; and unfortunately, by some extraordinary oversight, 
the instrument employed in the experiment, and made ex- 
pressly with that object, was unable to record any angle 
less than 15 0 . 
Those very angles which most concern aerial experi- 
menters were left out of the question. It may, however, 
readily be conceived that at less angles the resistance to the 
forward motion is less, consequently the power required to 
propel is less, except that greater velocity is required to 
keep the same weight in suspension. 
But we will take the calculations at 25 miles an hour 
and 15 0 , and 300 square feet of plane surface. At that 
velocity a rigid plane surface would support, at the least, 
450 lbs. : in reality much more than that, because the sup- 
porting effect of a plane increases in some yet undetermined 
ratio for each additional square foot. This, however, is not 
a rigid surface, and therefore some element of uncertainty 
exists. 
However, it appears to be necessary for success to be able 
to propel such a surface at the rate of 25 miles an hour. 
We have it reported that down an incline Mr. Linfield suc- 
ceeded in obtaining 20 miles an hour; but inasmuch as 
upon the level ground he did not travel more than 12 miles 
an hour, with the greatest number of revolutions which it 
was possible for him to impart by his muscular efforts to 
the screw-propeller, it is evident that the excess down 
the incline was due only to gravity. The additional air- 
pressure must have had the same effe< 5 t upon his screw- 
blades as the wind produces upon the sails of a windmill, 
thereby accelerating the speed of the screw without 
producing an increase of propulsive force, because the air 
would pass with a greater velocity than that at which the 
screw was working, rendering it impossible for him to keep 
his feet upon the treadles. The aid of an engine and rail- 
way would therefore be no assistance to anyone trying a 
similar experiment. It is, I think, conclusive that man has 
