379 



ON SWIMMING. 



BY PROFESSOR BORELLI, OF NAPLES*. 



Swimming may be considered as a certain species of flying ; the 

 motion in each case being performed in a fluid in which fishes and 

 birds of different kinds both move forwards supported in the same 

 manner as terrestrial animals are upon the ground. As the ancients 

 have not fully investigated the causes of these motions, nor the means 

 by which they are performed, we shall endeavour to supply what they 

 have omitted. 



In explaining the difference between flying and swimming, the object 

 of our inquiry is not the difference between the aerial and aqueous 

 fluid, but the manner in which birds and fishes move through the air 

 and water. It is evident that two operations are necessary in flying: 

 the first is the suspension of the body of the bird in the air, effected by 

 frequent leaps and by the great power of the pectoral muscles; the 

 second is the transverse motion of the bird which carries it forward in 

 flying. But animals that swim do not require any power to suspend 

 them, for they are supported by the specific gravity of the water so that 

 they cannot fall to the bottom, and therefore they can only move 

 through the water by the impulse of organs of motion peculiar to them- 

 selves. 



As to the differences in the modes of swimming, it is evident from 

 the doctrine of Archimedes, that bodies which float upon the surface of 

 water are not wholly immerged in it, but a part of them remains above 

 the water ; the weight of the water displaced by the body is equal to 

 the weight of the whole body, both the part under and that above the 

 water ; and the body is said to be of less specific gravity than water. 

 Bodies, which, wholly immersed, remain in any situation in the water 

 being of equal weight with the water they displace, are said to be of 

 the same specific gravity as water : and those bodies, which, when 

 wholly immersed, do not remain but sink to the bottom, are heavier 

 than an equal quantity of water, and are said to be of greater specific 

 gravity than water. 



* Translated from the Latin, by John Sharp, Esq., Bannockburn, near 

 Stirling. 



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