ON THE DIVING OF AQUATIC BIRDS. 167 
problem in natural history was perceived, and I was 
induced to make a few comments on the subject 
in my zoological note-book. It is probable, how- 
ever, that they never would have filled a more con- 
spicuous situation than that which they so long oc- 
cupied in its pages had not my attention been again 
directed to them by Dr. Drummond’s introduction 
of Montagu’s hypothesis, which is directly opposed 
to the established principles of dynamics, in his inter- 
esting ‘ Letters to a young Naturalist.’ 
It is asserted by the advocates of this hypothesis 
that the action of the legs in diving not only gives 
to birds a progressive motion, but also a tendency 
to rise; which tendency being overcome by the 
pressure of the water above them, the entire moving 
force is directed in the line of the body, accelerating 
thereby the velocity with which they pursue their 
subaqueous course. 
Now, it is a law of hydrostatics that the pres- 
sure of fluids in a state of equilibrium is equal 
in all directions at the same depth: whatever 
obstacle, therefore, the circumstance of pressure 
may present to the ascent of a bird when diving 
it must also present, ceteris paribus, to its progres- 
sive motion. 
Moreover, it is manifest, from the exceeding facility 
with which the particles of water move among one 
another, that if any tendency upwards did result 
from the action of the limbs of Water-fowl in diving, 
