It is the nature of waves--and a tide is a wave of a special kind--to move more slowly in crossing shallow water, rising at the same time to a greater height. Waves expend the energy of their motion when they increase in height, an effect which can be observed as they heap up before breaking as surf on the beach. So the tidal wave moves in from far offshore starting with relatively low ranges, some two or three feet at Sable Island off Nova Scotia, with similar readings in Bermuda and the Bahamas; but when it reaches the outer coast of the Cape it is augmented. To the southwest of the Cape the increase is only moderate, the figure for the entrance to Buzzards Bay being three and one half feet; but moving north it gets much higher. To reach the shores of the great embayment of the Gulf of Maine, formed where the coastline drops away north and east of the Cape, the ocean’s tidal wave must first cross the shallow waters of George’s Banks, a passage that requires more than three hours (which explains the later time of high water in the Bay). In the process the tidal height increases to the nine-foot figure, a reading which is true of Provincetown, Plymouth, and on up to the coast of Maine. So the Cape lies between two tidal systems, created and separated by its geography. On the south side, incidentally, there is a complex pattern of tidal movement caused by the fact that both systems meet. Tidal waves enter the sounds between the Cape and the islands of Martha’s Vineyard and Nantucket from two directions and pass each other. The combined effect of this “interference” results in rapid changes in the time and height of the tide between Monomoy and Woods Hole. Off Nobska Point one tidal wave movement is high, while the other passing it is low. Their interference results in the smallest range of tide (one and a half feet) to be found along the south shore. A similar minimum tidal range occurs off the southeast corner of Nantucket.