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leaping, is to the length of their body as 200 to 1. A flea leaps still far- 

 ther and more swiftly*. 



The larve, called the cheese maggot, forms itself into a circle, by con- 

 tracting, as much as possible, its abdominal muscular fibres: after hav- 

 ing, in this manner, brought near to each other its head and tail, it sud- 

 denly extends and straightens itself, and sends itself to a considerable 

 distance. It is by a similar mechanism, that the salmon, the trout, and 

 other fishes, swim against rapid currents interrupted by water-falls. They 

 bend their body, to a considerable degree, straighten it powerfully, and 

 thus overcome the obstacle which opposes their progress. I believe how- 

 ever, that in this particular case, the leap is not effected solely by the 

 straightening of the elastic curve, as is maintained by some authors, but that 

 it is likewise occasioned by the resistance against the water, of the tail 

 of the fish, which strikes it powerfully, at the moment of raising itself; 

 in the same manner, as in the northern seas, the enormous whale strikes, 

 with so sudden and violent a blow of her tail against the water, as to re- 

 ceive from it a fixed point, and rise to the height of fifteen or twenty feet, 

 as we are informed by navigators. Lobsters leap, by violently extending 

 their tail, an elastic and contractile arch, which they had previously kept 

 bent under their body. 



This theory of leaping would seem to be contradicted by what is relat- 

 ed by Professor Dumas, of a man without thighs, and who, neverthe- 

 less, performed surprising feats of dexterity and agility. But in this in- 

 stance, might not the pelvis, the vertebral column, and especially the 

 lumbar portion of the latter, make up, by a greater mobility, for the 

 want of the longest of the three levers formed by the lower extremity. 



In the act of leaping the body, which has received the impulse, may 

 rise in one of two ways, perpendicularly to the horizon, which constitutes 

 the vertical leap, or in a direction more or less oblique. The vertical 

 leap is always of less extent than that which takes place in an inclined 

 direction, and the latter is always greater, when it has been preceded 

 by running. In running before leaping, we have already acquired an 

 impulse which is added to that which the mechanism of leaping may 

 produce. 



To convince ourselves of the reality of this additional power, let us 

 recollect how difficult it is to stop suddenly, in the midst of a race, if 

 we have not previously slacked our pace. This impulse is one of the 

 causes which make runners fall forward, when the slightest obstacle 

 meets their feet; but whatever may be the force, the direction of leap- 

 ing, and the powers which produce it, the body by which it is executed 

 must be considered as a real projectile that is impelled, by a motion 

 counteracted by the force of gravitation. Whatever motions we may 

 perform, every thing depends on the first impulse; as soon as the feet 

 cease to be in contact with the plane which supports them, it is no long- 

 er in our power to augment the force of the leap or its swiftness. In 

 dancing, it is impossible to excel in cutting capers, unless one is ca- 



* Barthez states, in his work on mechanics, that the Arabs call this little insect the 

 father of leaping ; and tht't Roberval, a natural philosopher of considerable merit, had 

 written a work entitled de saliu pulcis. Such a subject, thought by the ignorant to sup- 

 ply matter only for idle and fruitles speculation, may furnish results highly interesting, 

 \vhen treated by an able man. In tenui labor. Author's /V<??e, 



2Z 



