THE TIDES OF THE BAY OF FUNDY—MURPHY. 53 
to twelve feet. In the Central Pacific the height is from two 
to four feet. The tidal wave becomes one of great strength 
where there are narrow channels to receive and discharge the 
waters. The movement may have the violence of a river tor- 
rent, when the entrance to bays is such as to temporarily dam up 
the waters, until the far advanced tide has so accumulated that 
it overcomes the resistance and passes on in a body. 
“In some cases the whole tide moves in at once in a few 
“creat waves; this happens especially at the mouths of rivers 
“where there is obstruction from sand bars and other favoring 
“circumstances about the entrance. The phenomenon is called 
“an eagre or bore. The most perfect examples are afforded at 
“the mouths of the rivers Amazon, Hoogley, (one of the mouths 
“of the Ganges) and Tsien-tang in China. In case of the last- 
“mentioned river the wave plunges on like an advancing 
“cataract four or five miles in breadth and thirty feet high 
“and thus passes up stream to a distance of 80 miles ata rate 
“of twenty-five miles per hour. The change from ebb to flow, 
“tide is almost instantaneous. Among the Chusan Islands, just 
“south of the bay, the tidal currents run through the funnel- 
“shaped firth with a velocity of sixteen miles an hour. In the 
“eagre of the Amazon the whole tide passes up stream in five 
“or six waves, following one another in rapid succession, and 
“each twelve to fifteen feet high.” Dynamic Geology, Dana. 
At St. Malo, near Cherbourg, France, and at Swansea and Chep- 
stow, in the English Channel, they reach the respective elevations 
of 36 and 50 feet. 
We might proceed with the following assumptions : 
1. The tidal wave is a wave of translation moving parallel 
to the coast which it is approaching. (Dr. Whewell, Admiral 
Fitzroy.) 
2. The tides are undulations or oscillations, and form cur- 
rents when obstructed by coast lines. (Airy, Jordan, Dana.) 
3. The currents of the ocean result from cosmical force of 
gravitation opposing terrestrial gravitation, and from vis 
inertic, or a crowding of the water in high latitudes, (Airy, 
Jordan, Enc.-Brit., Maury.) 
