Aerial JVavigalion. 17 



deal less resistance than depressed. V represents a valve, which is 

 a long, thin, narrow, and light strip or slip of pasteboard, stiffened 

 cloth, tin or metal, a little wider than to cover one interstice between 

 the wires that run parallel to the axle EE so as to overlap, and as 

 long as DD or EE. The side of the valve V, m, n, o, is to be 

 moveably attached or fastened to the wire m, n, o, on the under side 

 of the frame, so as to open about thirty or forty degrees downwards, 

 and then shut, The cross wires, parallel to AA and CC, are designed 

 to prevent its striking through, as well as its overlapping a little the 

 side DD. The valve V being hung, another valve of the same size 

 and shape is to be moveably fastened by one of its longest sides, to 

 the next wire towards the axle EE ; and another to the next and 

 so on till valves are moveably fastened to all the parallel wires, be- 

 tween the side of the frame DD and its axle EE. The valves are 

 to lap on the sides of the frame a little and overlap one another 

 sufficiently to be air tight. The valves being all moveably hung be- 

 tween the side of the frame DD and its axle EE by one of their 

 longest sides to the wires,' are to be restrained from opening any far- 

 ther than is required, by small strings or cords being fastened to their 

 other longest sides, and then attached to the side DD of the frame. 

 The valves, being all moveably hung and restrained between DD and 

 EE, the other half of the frame of the wing is to be similarly valved 

 and have the valves restrained by. small strings or cords to the side of 

 the frame BFB. The hanging of the valves must commence at the 

 side BFB and continue to the axle EE. aa, bfh, cc, and dd repre- 

 sent another similar frame, similarly wired and valved ; ee, its axle 

 or pivot. W represents a balance valve, gr, its balancing wire; when 

 the frame is to be hung with this kind of valves, it is to be wired only 

 parallel to its axle. The valves are to be attached on the under side 

 of the wings to the wires, so as nearly to balance ; their greater part 

 must hang down and be similarly restrained as the others; when they 

 shut, they must overlap a little and the materials of which they are 

 made must be pretty stiff. These two similar frames are to be hung or 

 fastened together at stuv, by hinges, susceptible of a motion upwards 

 and downwards. G^ and Gg represent strong semi^circular rods, 

 whose ends are attached or fastened to the under side of the axles 

 EE, ee, at HH and Jih, by hinges or small staples, so as to allow the 

 axles a balancing motion. I, i, I, i represent four joints in these semi- 

 circular rods, designed, when the sides of the wings BFB and bfb 

 are raised, as they are attached by hinges at s, t, u, v, to admit the 

 Vol. XXV.— No. 1. 3 



