CURRENTS AND WHALING. 513 



they exhibited of feeding near the surface instead of diving lower 

 down, as they are usually seen to do in lower latitudes : they were 

 constantly in sight, instead of being only seen at intervals. 



It will be readily admitted that the medusa, like other animals, has 

 its appropriate seasons of procreation, and it will appear probable that 

 the season at which we saw them in such numbers was that in which 

 they are brought forth most abundantly. So also, however low the 

 temperature of the water in which they delight, there is little proba- 

 bility that their increase goes forward when the regions in which we 

 met them are locked up in ice, and the genial light and warmth of 

 the sun is denied them. 



The food of the sperm whale will therefore be borne off to lower 

 latitudes by the polar streams in greater abundance at one season 

 than another, and this former season corresponds with that in which 

 these currents have their greatest force. The sperm whale, it must 

 be expected, will leave the higher latitudes and follow the currents 

 which transport his food. 



In conformity with this view, we find the habits of the sperm whale 

 migratory. The polar currents, as has been seen, disappear from the 

 surface in many cases, but do not cease to flow ; and even when felt 

 both at the surface and below, they wdll in approaching lower latitudes 

 have their higher temperatures near the surface. The medusa will 

 therefore descend in either case to greater depths, and the whale must 

 dive in quest of the food which in higher latitudes he could find at the 

 surface. We have seen in what a decided manner the polar currents 

 become or continue superficial at the southern promontories of the 

 continents. A similar cause operating to a less extent raises them if 

 submarine, when they are interrupted or impeded by islands, and 

 spreads water of low temperature over the surface. Here then, at the 

 proper season, the food of the wmale will be not only more accessible, 

 but more abundant within a given space, in consequence of the check 

 the velocity of the stream must experience. 



So also in the zones of calms we have seen that the matter borne by 

 the polar currents in all probability finds a resting-place ; and here 

 also, at fit seasons, the food of the whale must be abundant. Points 

 possessing either of these characteristics I have distinguished, as 

 before stated, by the name of nuclei. 



However satisfactory this theory may be in explaining the causes 

 of the migratory habits of the sperm whale, it is obvious that we do 

 not know enough of the natural history of his favourite food, nor of 



vol. v. 129 



