216 Wisconsin Academy of Sciences^ Arts and Letters. 



tucket by a tide from the north four hours younger, but of greater 

 range, so that it is superposed on the lesser. The origin of the 

 Arctic tide is not traceable for want of data in these waters, but 

 it ascends Baffin's Bay. 



These facts go to show that we have not one but a number of 

 primary tides, created in different ocaans, acting in perfect har- 

 mony and repeating their phases as regular as the moon. 



Observiag the different motion of the tides, we find that they 

 obey in a particular manner certain varying impulses. Primarily 

 they move east, then west, with a general tendency to and from 

 the equator, unless interrupted by obstructions ; and on the whole 

 they partake of a circular motion in time to repeat. 



The original motion is a most decisive one, not as though a 

 stone were thrown into the water, as the comparison is sometimes 

 made, but just the opposite ; the greater portion of a whole ocean 

 appears to heave and rise into a wave in the course of a few 

 hours. 



In particular cases the impulse and its direction are very marked 

 owing to local interferences, such as the Bay of Fundy, where the 

 tide reaches the coast with great rapidity through a tongue of very 

 deep water, then moves endwise to the east, meets with the ob- 

 struction of Nova Scotia, so that the wave is augmented to alarm- 

 ing dimensions, Bristol Channel and a number of other places are 

 subject to similar tides, but of less extent. On the other hand we 

 find some cases of this kind in the other direction, for instance the 

 entrance to Magellan Straits, where the tide attains a range of 40 

 feet and over. 



The foregoing are facts obtained from long observation and 

 careful investigation of the phenomena. More than 4,000 reliable 

 data were collected from tables such as " Bowditch's Kavigator,'^ 

 Imray & Son's "Lights and Tides of the World," and various 

 other equally reliable sources. These were all reduced to abso- 

 lute time (Greenwich time) and platted on charts in their respec- 

 tive places. The true places of the co-tidal lines were thus 

 obtained, and the result shows beyond a doubt that the charts 

 of co-tidal lines now in use are far from being correct. 



In Pliny's judgment the cause was the sun and moon. We 



