198 M.G. R. Dahlander on the Equilibrium of a Fluid Mass 
mersed in the current exactly under each mark. In explanation 
of the following Table, it is only necessary to add that the first 
column N shows the number of the mark on the plank; the 
second column D the distance, in inches, of that mark from the 
bank; the third column d the depth, in inches, of the stream 
at each mark; the fourth column the values proportional to 
2 sin 6 as read off on the ripple-meter ; and the last column v the 
velocities in feet per minute, of the current as calculated, on the 
hypothesis of \=7°5 inches per second, by formula (43) : 
2 sin 0. 
A 
0 
1 
2 
3 
a 
5 
6 
7 
8 
9 
0 
ft 
In conclusion it may be added that, if desired, more accurate 
ripple-meters might easily be devised, and by means of such the 
velocities of currents might be determined from the forms of their 
ripples with a degree of precision little, if at all, inferior to that 
possessed by the methods now in use. It is from a theoretical 
point of view, however, that the relation between waves and rip- 
ples, which we have endeavoured to establish, promises the great- 
est interest. For there can be little doubt that a skilful experi- 
menter, pursuing the subject in this direction, would greatly 
extend our present knowledge with respect to the changes in the 
velocity of a current at different points of its surface, and espe- 
cially with respect to the velocities with which different kinds of 
waves are propagated on the surface of still water, and to the 
variation of this velocity during the propagation of one and the 
same wave. 
January 15, 1861. 
XXX. On the Equilibrium of a Flud Mass revolving freely 
within a Hollow Spheroid about an Axis which is not its Axis 
of symmetry. By G. R. DAHLANDER*, 
+ we suppose a fluid ellipsoid to revolve alone about an axis 
which is not an axis of symmetry, we easily perceive that 
it cannot assume a position of equilibrium. It is, however, dif- 
* Communicated by the Author. 
