77 
DIVING BIRDS AT THE ZOO. 
Submarine boats, according to the naval architects, 
would be the fastest in the world, if only their crews 
could work them. This seems a hard saying ; but 
the fact can be proved by theory, and seen at work in 
nature. On the surface most of the work done goes 
to form waves. Below, no waves are made, as, for 
example, when salmon are travelling up a stream. 
There remains, of course, some resistance to the 
submerged boat or bird, but so much less than- on 
the surface, that, given the same driving power, the 
speeds below water are thrice or four times greater 
than above, the evidence of which proposition may be 
seen either in Mr. Froude’s experimental basin, near 
Fort Gilkicker at Stokes Bay, or any morning at 
12 o’clock in the glass tank in the Fish House at the 
Zoo, when the diving birds are fed. 
Unlike the submarine boats, all of which are more 
or less alike, the submarine birds show the most 
obvious and extreme differences of design, both in 
body and propelling machinery. Yet they all get 
their living in exactly the same way, by chasing and 
