PHENOMENA OF THE UNIVERSE. 137 



this circumstance, that although so great (for it is as I have 

 said fivefold), and that not in a transient, as in the vapours 

 of quicksilver, but in a consistent body, it returns without 

 difficulty to its former orbit. 



CONTINUATION OF THE HISTORY OF THE CONJUNCTION 

 AND EXPANSION OF MATTER THROUGH SPACE IN THE 

 SAME BODY. 



Animals in swimming depress the water with their hands 

 or feet ; that being depressed, rises above its natural con 

 sistency, and bears up the body rising upon it. But skilful 

 swimmers can so balance themselves upon the water, as to 

 keep themselves up for a time without moving their arms or 

 legs ; nay, to walk upright and on the water, and perform 

 other feats of agility. 



Waterfowls, indeed, are webfooted, and so can conve 

 niently depress the water with the membranes of their feet; 

 but can swim better in deep water. 



Birds in flying beat and condense the air with their 

 wings, but the air, (as was said of water) restoring itself 

 to its own consistency, carries the bird. And birds also 

 sometimes cut their path with expanded wings but retained 

 in one position, or now and then striking their wings a 

 little and then returning to their gliding motion. And 

 there is an analogy between winged animals, whether 

 feathered or not. For flies and all creatures of that kind 

 have their membranes of wings with which they beat the 

 air. But the weakness of their wings is made up by the 

 lightness of their bodies. Winged creatures are more easily 

 borne up aloft, especially those which have broader wings, 

 as the swallow, though their motion is not so swift. And 

 all birds which are of considerable magnitude have more 

 difficulty in the first stage of their flight, in elevating them 

 selves from the earth, since the air is of course not so 

 deep. 



CAUTION. 



The motion of condensation in water, or air, or the like, 

 is manifestly through striking or moving upon it. The 

 parts of air or water, the farther they are from the first 

 stroke or impulse, the weaker they are struck, and the 

 slower they give way; but as they are nearer, so much the 

 more forcibly and quickly; whence it necessarily happens 

 that the anterior air, which flies with more rapidity, comes 

 up to the posterior air, which is slower in its course, and so 

 they come together. But since a greater condensation than 



