180 OBSERVATIONS ON THE WINDS. 



" On tne contrary, I have no hesitation in saying that during eleven 

 months of the year there is a strong Northerly wind blowing down the 

 Coasts of Spain and Portugal, and further the prevailing wind in the 

 Mediterranean is from the North, and this is the way I account for the 

 supply of air being kept up that is necessary to fill up the vacuum caused 

 by the air ascending near the Line. 



" If this theory be true, it follows that' the great object of gathering the 

 data you wish our captains and others navigating the Atlantic to collect, 

 will be to determine where the hne of contact is at the different seasons ; of 

 course it will vary North or South according to the declination of the sun. 



" It would be of immense benefit to us to know that, on the passage out, 

 by keeping to the North we should ensure Northerly winds, and that 

 during the homeward passage a more Southerly course would keep our 

 ships in a South-Westerly wind." 



(111.) It seems quite clear that the steady Westerly winds spoken of by 

 Captain Inglis were experienced during the passage home, whilst the quick 

 changing circlets to which he alludes were met with on the outward passage, 

 which facts are borne out by Captain Martyn's log ; and the natural con- 

 clusion is that homeward the ship was moving with a wave or system of 

 weather, whilst outward she met several such waves. 



(112.) Temperature, &c. — It is a curious coincidence that the spot which 

 Captain Inglis speaks of as the Western limit of the great South- Westerly 

 Equatorial current of air is the position of the Eastern edge of the first 

 cold water met with on the outward passage, and where Northerly dis- 

 turbances seem to be very common in the wind. 



The effect of the Temperature of the surface water on the wind and 

 weather seems to be a phenomenon of universal occurrence ; in the warm 

 water on the Eastern edge of the Agulhas Bank the wind is notoriously 

 unsteady, insomuch that however fresh and fair the wind may have been 

 to a ship coming from the Eastward, she is almost sure to get bafiiing 

 unsettled weather in this warm water, and the clouds have a more tropical 

 doldrum appearance : whereas, in the patches of cold water in the Southern 

 Hemisphere, hail squalls from the S.W. are common (see my paper on 

 the Specific Gravity, Temperature, and Currents of the seas passed through 

 during five voyages from England to India, read before the Eoyal Geo- 

 graphical Society, May 8th, 1865), just as hail and snow-storms from the 

 N.W. are common in the cold water to the Eastward of North America, 

 and ships are said to run out of it into the warm water of the Gulf Stream 

 to refit after a fight with a winter gale. In fact, over cold and warm 

 water in close proximity, we have the same forces in operation as those 

 which enable land and sea-breezes to reverse the prevailing wind of the 

 season ; and if atmospheric pressure relatively increases over cold water, 

 then according to Buys-Ballot's Law, there would be a tendency to 

 Northerly winds on the Eastern edge of a patch of cold water in the 

 Northern Hemisphere, whilst Southerly winds would be more prevalent 

 on its Western edge, unless its effect be masked by greater influences. 



It will be noticed that from England to about 40° W. and 47° N. the 

 surface temperature is very uniform ; in diagrams 5 and 6 this Tiniform 

 temperature extends farther West ; then in about 49° W. a patch of cold 



