HYDROGRAPHY 153 



north and south, following the contours of the continents and 

 of the floor of the ocean. 



These are some of the more important results in regard 

 to the distribution of temperature in the sea discovered by 

 the " Challenger " expedition and by other oceanographers 

 since ; but it must be pointed out that there are also excep- 

 tional cases, or variations from the normal arrangement, 

 due to unusual causes, probably in some cases of periodic 

 occurrence. These give rise to occasional increase or diminu- 

 tion of known oceanic currents, and the consequent inflow of 

 water of unusual character into an area — and this is generally 

 first recognized from the strange organisms accompanying 

 the water. 



As an example of another occasional influence affecting the 

 temperature of the water, there is the effect of wind. Sir 

 John Murray, and others since, have shown the well-marked 

 effect of prevalent winds upon the distribution of tempera- 

 tures in the Scottish lochs or in narrow fjord-like arms of 

 the sea. Murray, for example, showed that in Loch Lochy, 

 in April, 1887, after a south-west gale, the warmer surface 

 water was driven away from the south end of the loch and 

 was piled up at the north end, displacing colder water down 

 to a depth of 10 fathoms. Water of intermediate tempera- 

 ture was also carried away from the south end and accumu- 

 lated farther north down to a depth of 25 fathoms, so as to 

 allow colder bottom water to come to the surface at the south 

 end of the loch. In Loch Ness, on the same occasion, he 

 found even a more extreme condition, where the bodies of 

 water of three temperatures formed almost vertical columns, 

 the warmer at the leeward (north) end, the colder at the 

 windward (south), and the water of intermediate temperature 

 in the middle of the loch (see Fig. 7). 



A similar effect may be produced on the sea coast where a 

 strong off-shore wind will carry out the surface water, with 

 its contained organisms, and so allow deeper water to well up 

 close inshore (Fig. 8) . Even in the open ocean, in places and 



