52 2 TEE POPULAR SCIENCE MONTHLY 



When Newton had made public his capital discovery, and had shown 

 that the magnitudes or ranges of the tides increase and decrease in 

 accordance with the varying attractions of the moon and sun, the tidal 

 problem was supposed to be nearing a solution. Indeed, Newton 

 thought that he could see in the observed times of tides upon certain 

 shores a justification of his theoretical considerations. His work, how- 

 ever, was only a beginning. Since his time, eminent mathematicians, 

 astronomers and physicists — including Bernoulli, Maclaurin, Euler, 

 Lalande, Laplace, Young, Lubbock, Whewell, Airy, Ferrel, Kelvin, Dar- 

 win, Levy and Hough — have addressed themselves to this subject ; while 

 others, like Lagrange, Stokes, Eayleigh, Lamb and Poincare, have dealt 

 rather with the underlying mathematical and physical problems. 



Since it has been universally recognized that the tides result from 

 the attraction of the moon and sun, the popular mind has taken little 

 interest in the manner in which these forces operate in order to pro- 

 duce the tides. The apparent hopelessness of the task has doubtless 

 deterred many investigators from devoting to it a full measure of their 

 attention. In fact, as will be shown below, there is no such thing as 

 " the tidal problem " analogous to the astronomers' " problem of three 

 bodies." The tide involves a number of problems, and to even discover 

 what these problems are requires a good knowledge of the forms, sizes 

 and depths of the oceans, together with a knowledge of the tide-pro- 

 ducing forces. The observed tides themselves render great assistance 

 in this matter; for their times and ranges indicate the ways in which 

 the various oceans probably oscillate, and so, in a measure, the under- 

 lying tidal problems requiring solution. 



General Belief in a Westwaedly-progeessing Tide Wave 

 Various theories were instrumental in leading to the belief of a gen- 

 eral westward progression of the tide. As before the Copernican 

 system of astronomy became known or generally accepted, the tides 

 were made to accord with the Ptolemaic system then prevailing, so for 

 some time before and after the publication of Newton's " Principia," 

 the tides were made dependent upon the vortices of Descartes's theory. 

 The Ptolemaic system of astronomy assumed the center of the earth 

 to be the fixed center of the universe around which revolved a series of 

 concentric spheres. The outermost of these was styled the primum 

 mobile; this by its westward motion imparted westward motion to the 

 stars and other heavenly bodies, to the atmosphere, and even to the 

 waters of the oceans. And so before the law of gravitation was estab- 

 lished, the notion became prevalent that water had a westward motion 

 (ah oriente in occidentem or ah ortu in occasum) around the globe; 

 and because the flood stream, rather than the ebb, was the one chiefly 

 considered, the flood stream (and so the progression of the tidal wave) 

 was commonly supposed to partake of this westward motion. The 



