46 LIMITS OF HUMAN POWER. 
one continuous blast, or the momentum expended by the waves, 
in a tempestuous winter, upon the breakwater at Cherbourg,* 
or the lifting power of the tide, for a month, at the head of the 
Bay of Fundy, or the pressure of a square mile of sea water at the 
depth of five thousand fathoms, or a moment of the might of 
an earthquake or a volcano, our age—which moves no moun- 
tains and casts them into the sea by faith alone—might hope 
to scarp the rugged walls of the Alps and Pyrenees and Mount 
Taurus, robe them once more in a vegetation as rich as that of 
their pristine woods, and turn their wasting torrents into re- 
freshing streams.t 
Could this old world, which man has overthrown, be rebuild. 
* In heavy storms, the force of the waves as they strike against a sea-wall 
-is from one and a half to two tons to the square foot, and Stevenson, in one 
instance at Skerryvore and in another at the Bell Rock lighthouse, found this 
force equal to nearly three tons per foot. 
The seaward front of the breakwater at Cherbourg exposes a surface of 
about 2,500,000 square feet. In rough weather the waves beat against this 
whole face, though at the depth of twenty-two yards, which is the height of 
the breakwater, they exert a very much less violent motive force than at and 
near the surface of the sea, because this force diminishes in geometrical, as 
the distance below the surface increases in arithmetical, proportion. The 
shock of the waves is received several thousand times in the course of twenty- 
four hours, and hence the sum of impulse which the breakwater resists in one 
stormy day amounts to many thousands of millions of tons. The breakwater 
is entirely an artificial construction. If then man could accumulate and con- 
trol the forces which he is able effectually to resist, he might be said to be, 
physically speaking, omnipotent. 
+ Some well-known experiments show that it is quite possible to accumulate 
the solar heat by a simple apparatus, and thus to obtain a temperature which 
might be economically important even in the climate of Switzerland. Saus- 
sure, by receiving the sun’s rays in a nest of boxes blackened within and coy- 
ered with glass, raised a thermometer enclosed in the inner box to the boiling 
point; and under the more powerful sun of the Cape of Good Hope, Sir John 
Herschel cooked the materials for a family dinner by a similar process, using, 
however, but a single box, surrounded with dry sand and covered with two 
glasses. Why should not so easy a method of economizing fuel be resorted to 
in Italy, in Spain, and even in more northerly climates? 
The unfortunate John Davidson records in his journal that he saved fuel in 
Morocco by exposing his teakettle to the sun on the roof of his house, where 
the water rose to the temperature of one hundred and forty degrees, and, of 
