The power is represented by the wing, the fulcrum by the air, and the weight by the body of the flying animal.
Although the third order of lever is particularly inefficient when the fulcrum is rigid and immobile, it possesses singular advantages when these conditions are reversed, that is, when the fulcrum, as happens with the air, is elastic and yielding.
When the wing ascends as shown at p, the air (fulcrum f) resists its upward passage, and forces the body (b) or its representative (w) slightly downwards.
The beam is of bronze in a single deep casting, cored out in the middle so as to allow the saddle at the top of the stand to pass through the beam and afford a continuous bearing for the fulcrum knife-edge.
The pair of beams are hung centrally by rods and hooks from knife-edges in the forked end of a strong beam, which is carried at its fulcrum by the top plate of the frame of the machine.