THE TROCHOIDED PLANE. 69 
need reversing gear, and the pitch could be made easily adjust- 
sabe by te the length of the connecting-rods of the propellers, 
we take two floats that offer equal lateral resistance 
the vertical longitudinal section ; then put a rotating crank with 
the shaft vertical in the centre of one of the floats, and a guide of 
some description on the bar of the other float ; unite the end of 
the bar from the crank-float to the guide, and the end of the bar 
of the float that carries the guide to the crank-pin, and it will be 
seen that the whole apparatus will be propelled through the water 
by rotating the crank ; this is like a common feat with skates on 
Two wheels may be substituted for each plane in this model 
for motion on a surface, but the results are unsatisfacto 
a pair of equal floats be made with a total displacement 
age that of a man, it will be found that crank, guides, and 
ecting-rod can be dispensed with, and that the floats can be 
tschoided by the feet. The steering is effected by bearing a little 
mechanism will commend this form of exercise, and I hope to see 
it become a —— in our Lihat 
ut these experiments are not calculated to convey to every eye 
the identity. of the RIT plane with the cee ant power used 
by a fish in swim , So it was thought necessary to make some- 
thing with a ecaaals likeness to a fish, ‘and cut it up into a pone 
of rv and unite the sections again so that they were fre 
move from side to side on vertical hinges (Fig. IV). Each pest 
was tepecrrive underneath with a keel, pre every alternate section 
was made equal to the amplitude of the trochoidal waves it was 
intended the model should use, and the pitch was made equal to 
the wave length. The forward end of the helix was brought into 
the ewe, as if it had been twisted round a spindle instead of a 
planes together, and made the model swim in a strikingly natural 
manner ; by drawing the model tail first through the water, the 
operation is reversed, and the trochoided planes wind up the 
spring. This model is remarkable for the diminutive nature of 
the motive Sener, in easy trochoiding of the planes, and the 
| percen of sli 
Here, I ca ane that a running stream offers a good field 
for investigation on this subject ; however straight its channel is 
cut, it will, if left to itself, meander, and the bends work down 
