70 THE TROCHOIDED PLANE. 
eam. This may be best seen when the stream runs through an 
alluvial flat ; it will be observed that the down stream sides of 
the bends are continually being washed away, and that ‘deposits 
are made on the down stream sides of the points. 
If the upper ends of the guides in the last-described model be 
connected to a rigid bar, the motion of the helical wire will make 
the guides, or an elastic web covering them, take the form of a 
fin, showing the action I have previously described. 
Again, if a number of pieces of wood be rove loosely across a 
rotating helical wire, the ends of the pieces will be trochoided like 
the legs of a centipede; owing to difficulties about making the 
clawing apparatus, this was made to float in water, and you had 
an opportunity of judging ior yourselves whether or not it proved 
the truth of my deductions.* 
I will now direct your attention to the swimming of that com- 
ring ; t 
and backwards when most expanded ; the superficial resultant 
being annular or cylindrical trochoidal waves thrown backwards, 
and motion of the jelly-fish forwar 
e progress of an earth-worm ‘through a cylindrical hole is 
another obvious case of cylindrical waves, and from the worm’s 
movement on a flat surface it appears capable of throwing more 
than one wave towards its tail at the same time, or, in other words, 
that its body is longer than a wave length ; in this case the motion 
of the rings is evidently not circular, as in a smoke ring, but very 
elliptical, with oe major axis parallel to the direction of propaga- 
tion of the wav: 
If you note en mechanical action of swallowing, it will = 
evident that it is rap converse of the motion of the worm; obse 
the jaws or mouth opened and thrust forward, closed and soars 
back for a fresh bite, the prey being none to the stomach by a 
similar movement of the rings of the 
The trochoidal action of fins, muscles, uit legs, seemed so plain 
that I could not help being led to theorize on the action of wings 
in flight ; I say theorize simply because I have not a flying-machine 
to show you, but the chain of evidence seems so complete, that I 
have no doubt it will soon be accomplished without the aid of the 
Screw or gas bag. 
The wings of flying-fish are, in my opinion, only used for flight, 
or when the fish is swimming very slowly with its fins alone, with- 
out ee its bod, 
° Sap il va ws Gl a aa i PO 
