NATURE NOTES 
1 86 
than salt water, fresh water lakes have on the whole larger waves 
than bodies of sea water of proportionate size. On Lake 
Superior, for instance, we not only experience violent storms 
with lofty waves, but all the familiar permanent results of wind 
and wave action, beaches, sand-dunes and cliffs, are represented 
along the shores. 
A gale in the open ocean will lash up the waters into spray 
and produce waves which seem of prodigious height to un- 
fortunates in any small boat ; but few of our impressions are 
more misleading. Dashed from their crests into the troughs 
between, we say the waves ran “ mountains high ; ” but the 
highest waves in British seas probably never exceed fifteen or 
twenty feet, and the greatest height observed by Scoresby in 
the waves of the Atlantic was but forty-three feet. This is, of 
course, the height of the wave from trough to crest and has 
nothing to do with the height to which spray, water or stones 
may be hurled when the waves break on the shore. 
The wave-movement produced in a storm is prolonged for 
some time after the wind has lulled, and to a great distance 
beyond the original area of disturbance, not as waves with 
broken crests of spray, but as the broad and long heaving un- 
dulations known as ground-swell. Here again appearances are 
deceitful, and it is difficult to convince oneself of the small 
transporting effect of these great waves in the open sea. As in 
ordinary waves in similarly deep water, the actual movement 
of the water is mainly up and down, its particles travelling in a 
curve resembling an attenuated figure of eight. This explains 
why, unless they get into some ocean-current, bottles thrown 
overboard, or other floating objects, travel so slowly across the 
surface of the ocean. 
Where the water becomes shallower near shore, the upper 
part of the great heaving mass of water produced by ground- 
swell over-rides the lower, retarded as is the latter by the friction 
with the bottom, and the huge billow curves over and bursting 
into foam and spray, is known as a breaker. The same name, 
however, is applied to ordinary waves, produced by the imme- 
diate impact of to-day’s wind, when they break upon sunken 
reefs. All waves in shallow water become what is termed 
“ waves of tranlsation,” and we then see them carry shingle 
along the sea-bed, and floating bodies on their surface rapidly 
towards the shore. 
On a shingly shore, though the limits of the beach may be 
mainly determined by the tides, each wave may be seen con- 
tributing its share of work in the grinding-down of flints or 
other masses of hard rock into smaller and rounder pebbles and 
sorting them according to their size. The deafening rattle of the 
undertow, as the wave, retreating from the shelving shore, drags 
back with it these myriad pebbles, may give us some notion 
of the forces of friction and percussion thus exerted in breaking, 
chipping, rounding, and polishing. 
