J. R. Mayer on Celestial Dynamics, 403 
from the magnetic meridian, and which, while tending to return 
thereto, exerts a constant lateral pressure. 
The foregoing discussion may suffice to demonstrate the in- 
fluence of the moon on the earth’s rotation. The retarding 
pressure of the tidal wave may quantitatively be determined in 
the same manner as that employed in computing the precession 
_of the equinoxes and the nutation of the earth’s axis. 
ried distribution of land and water, the unequal and unknown 
depth of the ocean, and the as yet imperfectly ascertained mean 
difference between the time of the moon’s culmination and that 
of high water in the open sea, enter, however, as elements into 
such a calculation, and render the desired result an uncertain 
quantity. 
In the mean time, this retarding pressure, if imagined to act 
at the equator, cannot be assumed to be less than 1000 millions 
following calculations. 
he rotatory: velocity of the earth at the equator is 464 metres, 
and the consumption of mechanical work, therefore, for the 
maintenance of the tides, 464,000 millions of Km, or 6000 mil- 
lions of horse-powers per second. The effect of the tides may _ 
consequently be estimated at =+,th of the effect received by the 
~~ The pelédities of rotation of a sphere stand to each other in 
the same ratio as the square roots of the rotatory effects, when 
the volume of the sphere remains constant. From this it fol- 
lows that, in the assumed time of 2500 years, the length of a 
day has increased —4,,th; or if a day be taken equal to 86,400 
Seconds, it has lengthened 1th of a second, if the volume of 
the earth has not seanped: "Whether this supposition be eee 
_ ©r not, depends on the temperature of our planet, and wi 
discussed in the next chapter. 
~ The tides also react on the motion of the moon. The stronger 
attraction of the elevation nearest to, and to the east of the 
