398 J. R. Mayer on Celestial Dynamics. 
parts of the earth’s surface, and by the axial rotation of our 
be 
obe. 
The alternate rising and falling of the level of the sea may be 
compared to the ascent and descent of a pendulum oscillating 
under the influence of the earth’s attraction. 
The continual resistance, however weak it may be, which an 
instrument of this nature (a physical pendulum) suffers, con- 
stantly shortens the amplitude of the oscillations which it per- 
forms; and if the pendulum be required to continue in uniform 
motion, it must receive a constant supply of vis viva correspond- 
ing to the resistance it has to overcome. 
Clocks regulated by a pendulum obtain such a supply, either 
from a raised weight or a bent spring. The power consumed i 
raising the weight or in bending the spring, which power is rep- 
resented by the raised weight or the bent spring, overcomes for 
a time the resistance, and thus secures the uniform motion of 
the pendulum and clock. In doing so, the weight sinks down 
or the spring uncoils, and therefore force must be expended in 
winding the clock up again, or it would stop moving. 
Essentially the same holds good for the tidal wave. The 
moving waters rub against each other, against the shore, and 
against the atmosphere, and thus, meeting constantly with resist- 
é ° come to rest if a vis viva did not exist compe 
tent to overcome these obstacles. This vis viva is the rotation 
of the earth on its axis, and the diminution and final exhaustion 
thereof will be a consequence of such an action. : 
The tidal wave causes a diminution of the velocity of the rotahon 
of the earth. 
This important conclusion can be proved in different ways. 
The attraction of the sun and the moon disturbs the equili- 
brium of the movable parts of the earth’s surface, so as to move 
the waters of the sea toward the point or meridian above and 
however, the moving water esistance, in conse- 
rs experience r : 
quence of which the flow of the tidal wave is delayed, and high 
water occurs in the open sea on the average about 24 hours after 
: waters, but also in a slow progressive motion from east 
