90 



SCIENCE. 



[N. S. Vol. II. no. 30. 



curve, concave towards the equator. Simi- 

 larly, -witli reference to tlie southern hemi- 

 sphere, as viewed from the equator, the sub- 

 marine flow from the pole would assume a 

 northwesterly curve, convex towards the 

 equator, and the supra-marine flow from 

 the equator to the pole would assume a 

 southeasterly curve, concave towards the 

 equator. The reason for this is that the 

 sub-marine flow, coming from the north or 

 the south pole, would reach successively 

 degrees of latitude of greater and greater 

 velocity of rotation, and therefore would as- 

 sume a more and more westerly dfrection, 

 whereas the flow going from the equator 

 towards either pole would successively 

 reach degrees of latitude of less and less 

 velocity of rotation, and therefore would 

 assume a more easterly direction. 



The very same causes are operative now 

 to produce the very same efi'ect, and the 

 chief reason that it does not exist in the sim- 

 plicity described is on account of the pres- 

 ence of continental lines disposed in a 

 northerly and southerly direction. Yet, 

 despite the complication thereby introduced 

 into the phenomenon of ocean movement 

 by that and other causes, the surface waters 

 of the ocean, without regard to the streams 

 coursing through them, move in a general 

 direction in the northern hemisphere to- 

 wards the northeast, and the sub-marine 

 waters towards the southwest; while, in 

 the southern hemisphere, they move corre- 

 spondingly, the surface waters towards the 

 southeast, and the sub-marine waters to- 

 wards the noi'thwest. Owing to the causes 

 which have now been detailed at sufficient 

 length, the sub-marine waters lag behind 

 the surface waters, and therefore the sur- 

 face flow from the equator to the poles as- 

 sumes a relatively easterly position with 

 respect to the sub-marine flow from the 

 poles to the equator. The inclusion of the 

 agency of the north and south continental 

 lines, and the presence of constant winds 



in certain quarters of the eai-th, do not 

 create the movements of the oceans, but 

 merely serve to modify with great intricacy 

 the general flow. 



The movements just described as dedu- 

 cible from general principles, and long pre- 

 viously held to be true, have in quite recent 

 times been proved time by various scientific 

 observations, notably by those of the Brit- 

 ish ship Challenger, Captain Nares, in 

 1873-1876. Having thus settled once for 

 all in our minds that the primary cause of 

 the Gulf Stream is not the influence of the 

 ti-ade winds, to which it has long been as- 

 cribed, but that it is derived from causes 

 which were the basis of theory broached 

 manj^ years ago, the correctness of which 

 is fully established, let us proceed to intro- 

 duce for the completed phenomenon the 

 chief subsidiary agencies which make the 

 Gulf Stream what it is as observed. 



The Equatorial Current is known techni- 

 cally as a drift current, that is, one formed 

 by the friction of the wind on the surface 

 of water. The Equatorial Current is, in 

 consequence, not a deep current. Accord- 

 ing to Sir Charles Wyville Thomson, scien- 

 tific director of the Challenger expedition, 

 its movement does not reach below fifty 

 fathoms in depth. Moreover, it is not, as 

 commonljf spoken of, a single current, but 

 is divided into a northern and a southern 

 stream. The thermal equator does not 

 coincide exactly with the geographical 

 equator, but lies two or three degrees north 

 of it. In consequence, as the trade winds, 

 the cause of the Equatorial Currents, blow 

 from the northeast and southeast, the posi- 

 tion of those winds is determined by that of 

 the thermal equator, and the whole equa- 

 torial system of winds and currents tends 

 more to the north than to the south of the 

 equator, the southern limit of the northeast 

 trade winds, with the southern declination 

 of the sun, not reaching, by two or three 

 degrees, to the geographical equator, while, 



