THE 



POPULAR SCIENCE 



MONTHLY. 



JUNE, 1909 



THE TIDES: THEIR CAUSES AND EEPRESENTATION 



By ROLLIN ARTHUR HARRIS 



THE UNITED STATES COAST AND GEODETIC SDRVET, WASHINGTON, D. C. 



Historical Note on the Tidal Problem 



THE so-called problem of the tides has for ages engaged the atten- 

 tion of observing and thinking men. Before Newton established 

 the law of universal gravitation, the whole subject was surrounded with 

 an air of mystery, although the fact had long been recognized by many 

 that in some manner the tides are governed by the moon or the moon 

 and sun. Such views were held by Pytheas of Massilia, Seleucus of 

 Babylonia, Posidonius the Stoic philosopher, Caesar, Cicero, Strabo, 

 Seneca, Pliny the elder, Lucan, Claudianus and Macrobius. 



The ancients say little as to the agency whereby the moon is enabled 

 to exert an influence upon the waters of the globe ; but winds produced 

 by the moon, vapors surrounding the moon and the special power of 

 the moon to replenish moist bodies, are severally mentioned as being 

 the probable means. 



However, before Newton's great discovery, several philosophers had 

 gone so far as to suggest or assert that the tides are due to an attractive 

 force of the moon analogous to magnetic attraction. Among these 

 were Scaliger, Gilbert, the College of Jesuits at Coimbra, Antonio de 

 Dominis, Stevin and especially Kepler. 



Of course, not all ancient or medieval theorists admitted the moon 

 to be the cause of the tides. Some of the many other causes brought 

 forward were: The discharging of rivers into the sea; variations in 

 depths and densities of the sea ; the surface of the sea not being every- 

 where upon the same level; the respiration of the earth; submarine 

 caverns; submarine heat; submarine vapors, exhalations, or fermenta- 

 tions; power exerted by a supernatural being; whirlpools and eddies; 

 and the non-uniform motion of the earth or of its various parts. 



VOL. LXXIV. — 34. 



