238 MARINE BIOLOGICAL LABORATORY. 



tor to go towards the pole, it passes from a region of 

 great velocity of rotation to one where a lesser velocity 

 is found, and consequently gradually drops back to the 

 right or left, as the case may be. So, too, the water of 

 the pole, as it moves towards the equator, is constantly 

 advancing from a region of small velocity to a greater 

 one, and consequently gains in longitude as it goes on. 



Upon examination of any good map of the currents 

 of the oceans, it will be found that they follow this law 

 in their circuits without regard to the coast lines, though 

 the coasts materially change their directions in many 

 instances. This is particularly true of the southern por- 

 tions of the Atlantic, Pacific, and Indian Oceans, where 

 the courses of the currents are not interfered with by 

 the land masses of the globe, and are perfectly free to 

 move according to the law which controls them. 



We shall now consider some of the causes of these 

 currents, and the various theories which have been held 

 concerning them. Magnetism and the moon have been 

 a great source of comfort to people perplexed over the 

 difficulties presented by some of the phenomena of 

 nature. It was only recently that I saw an attempt 

 to explain the currents by the use of the laws of 

 magnetism. 



Among the earliest explanations we have of these 

 currents are those given by Kepler and Leonardo da 

 Vinci. Kepler believed they were due to the rotation 

 of the earth, while da Vinci thought they were caused 

 by a disturbance of the thermal equilibrium at the 

 equator. I will only take time to allude to one of the 

 many curious explanations given by the older geog- 

 raphers of these currents. Vossius, whose map I have 



