THE HANGCHOW BORE
istence of the bore as well as its fluctuations probably depends on a nice balance between various factors, and the irregularity in the depth and form of the estuary renders impossible the exact calculation of the form of the rising tide. The heading back of the sea water by the natural current of the river, and the progressive change in shape of a wave advancing into shallow water, may combine to produce a rapid rise of the tides in rivers. "But the explanation of the bore as resulting from these causes is incomplete because it leaves their relative importance indeterminate, and serves rather to explain a rapid rise than an absolutely sudden one." "It seems impossible from the mere inspection of an estuary, to say whether there would be a bore there; we could only say that the situation looked promising or the reverse." "... as in many other physical problems, we must rest satisfied with a general comprehension of the causes which produce the observed result." The description we have attempted may serve to give those who have not seen such a wonder some idea of the really marvelous phenomenon, but the best way to become familiar with its characteristics is to go and see it for yourself.