Somerville’s physical geography. 
153 
“ The tide in the open ocean is merely an alternate rise and fall of the water, so that 
the wave travels, but not the water. A bird resting on the surface is not carried forward 
as the waves rise and fall; indeed, if so heavy a body as water were to move at the rate 
of 1000 miles in an hour, it would cause universal destruction, since in the most violent 
hurricanes the velocity of the wind scarcely exceeds 100 miles in an hour. 
“ During the passage of the wave in deep water, the particles of the fluid for the mo¬ 
ment glide into a new arrangement, and then return to their places ; but this motion is 
extremely limited. In the ocean the resistance of the bottom is imperceptible; but in 
shallow water, where the velocity of the wave is small, its lower parts are more retarded 
than those above, and as the friction continually increases with the progress of the wave, 
its top advances more rapidly than the water below, so that over shallows and near the 
land both water and waves advance during the flow of the tide, and roll on the beach. 
“ The height to which the tides rise depends upon the form of the shores and bottom 
of the sea, and the direction in which the wave strikes the land. Throughout the Atlantic 
the height is 10 or 12 feet; but the tidal wave rushes so directly into the Bay of Fundy, 
that it rises to 50 feet, and from the shelving shores in the Bristol Channel it is 40 feet. 
When the tide enters the North Sea, to the north of Scotland, its height is 12 feet; but 
in travelling south along the east coast of England over a continually shelving shore, 
and striking the land always more directly, the water rises higher and higher at each place 
till in the Humber it attains 20 feet. 
“It sometimes happens that two equal tides coming different ways meet, and then the 
water rises to double the height it would otherwise have done. A complete extinction of 
the tide takes place when a high water interferes in the same manner with a low water, 
as in the centre of the North Sea,-—a circumstance predicted by theory and confirmed by 
Captain Hewett, who was not aware that such an interference existed. When two unequal 
tides in contrary phases meet, the greater overpowers the lesser, and the resulting height 
is equal to their difference, which is supposed to be the case at Yarmouth, where the tide 
Is very small. These varieties occur chiefly in channels among islands and in the estu¬ 
aries of rivers. When a tide flows suddenly up a river incumbered with shoals, it checks 
the descent of the stream ; the water spreads over the sands, and a high-crested wave, 
called a bore, is driven with force up the channel. This occurs in the Hoogly mouth of 
the Ganges, and in the Amazon at the equinoxes, where, during three successive days, 
five of these destructive waves, from 12 to 15 feet high, follow one another up the river 
daily; and it occurs in a less degree in some of our British rivers.” 
In the chapters immediately following those from which we have 
just quoted, Mrs. Somerville enters on the discussion of numerous im¬ 
portant subjects, which the limited space at our disposal does not permit 
us to consider. Such, for example, as lakes and rivers, the temperature of 
the earth, the atmosphere, winds and currents, terrestrial magnetism, &c. 
We pass on, therefore, to notice those portions of her work which treat of 
the distribution of organic life over the surface of the globe. In these may 
be found a vast aggregation of important facts, compiled in most cases 
from sufficiently authentic sources, hut too frequently huddled together 
in an incongruous and disorderly manner. The botanical chapters con¬ 
tain, perhaps, a smaller proportion of errors than most other parts of the 
book. The following passage, taken from her account of the Flora of 
tropical America, may he regarded as an example of Mrs. Somerville’s best 
style, though garnished, it is true, with her usual extensive assortment 
of adverbs and adjectives 
“ No language can describe the glories of the forests of the Amazon and Brazil, the end¬ 
less varieties of form, the contrasts of colour and size : there even the largest trees bear 
brilliant blossoms,—scarlet, purple, blue, rose-colour, and golden yellow are blended with 
every possible shade of green. Majestic trees, as the Bombax ceiba (or silk-cotton tree), 
