CHAP, iv.] TUMBLERS. FEATS OF WING. 113 



line, that would satisfy Euclid as being the shortest 

 distance between two points, to circles and ellipses that 

 remind us of the choreal orbits of the planets round 

 the sun ; but the Tumbler, while it is rapidly wheeling 

 past some sharp corner in a tightly-compressed para- 

 bola, seems occasionally to tie a knot in the air through 

 mere fun ; and in its descents from aloft, to weave 

 some intricate braid, or whip-lash. This latter per- 

 formance, I suspect, is quite a leger-de-vol, or sleight of 

 wing ; the bird does now and then tumble heels over 

 head, and perform somersets, which the best clown at 

 Astley's would be unwilling to risk at the same alti- 

 tude above terra firma for example, on the tip of 

 a cathedral spire, or in the car of a balloon but 

 many of these intricate weavings are the result of 

 some trick, best known to the performer, the real 

 solution of which may be suspected to be the 

 non-coincidence of the apparent centre of gravity of 

 the bird with its real one. The Indian jugglers have 

 a similar feat, in throwing a ball in a spiral course 

 instead of in an acute parabola, more or less approach- 

 ing to a vertical straight line ; and the laws of motion 

 would assure us that, with a homogeneous ball, such a 

 feat is impossible, under the existing circumstances of 

 the universe. But take a large hollow sperical shell, 

 heavily loaded internally at one point of its circum- 

 ference with* lead, so that the centre of gravity of the 

 mass is by no means in the centre of the hollow sphere, 

 and a clever juggler, by a dexterous twist, will make it 

 play strange freaks. Just so, the wings and tail of the 

 Tumbler are made to follow the impulse which them- 

 selves have given, and to revolve round the solid body 



