ON AERIAL NAVIGATION. 



171 



in the foreshortened posture of sitting to work his oars, he 

 will probably receive less resistance than the crow. 



It is of great importance to this art, to ascertain the real Solid of least 

 ,. , „ . . , , , ,, , 11- resistance re- 



sohd of least resistance, when the length or breadth is quires to be de- 

 limited. Sir Isaac Newton's beautiful theorem upon this temiined. 

 subject is of no practical use, as it supposes each particle of ^-^g^^jg^j^ 

 the fluid, after having struck the solid, to have free egress ; 

 making the angles of incidence and reflection equal parti- 

 cles of light seem to possess this power, and the theory will 

 be true in that case; but in air the action is more like an 

 accumulation of particles, rushing up against each other, in 

 consequenceof those in contact with the body being retarded. 

 The importance of this subject is not less than the difficiri- 

 ties it presents ; it aifects the present interests of society in 

 its relation to the time occupied in the voyages of ships ; it 

 will have still more effect when aerial navigation, now in its 

 cradle, is brought home to the uses of man. 1 shall state a 

 few crude hints upon this point, to which my subject has so 

 unavoidably led, and on which I am so much interested, and 

 shall be glad if in so doing I may excite the attention of 

 those, who are competent to an undertaking greatly beyond 

 my grasp. 



Perhaps some approach toward ascertaining the actual Mode of con. 

 solid of least resistance may be derived from treating the ^'''^nngth.e 

 subject in a manner something similar to the following. 

 Admit that such a solid is already attained (the length and 

 width being necessarily taken at pleasure). Conceive the 

 current intercepted or disturbed, by the largest circle that 

 can be drawn within the given spindle, to be divided into 

 concentric tubular laminae of equal thickness. At what- 

 ever distance from this great circle the apex of the spindle 

 commences, on all sides of this point the central lamina will 

 be reflected in diverging pencils, (or rather an expanding 

 ring,) making their angles of incidence and reflection equal. 

 After this reflection they rush against the second lamina and 

 displace it: this second lamina contains thiee times more 

 fluid than the first; consequently each pencil in the first 

 meets three pencils in the second; and their direction, after 

 the union, will be one fourth of the angle, with respect to 

 the axis, which the first reflection created. In this direction 



these 



