182 OBSERVATIONS ON THE WINDS. 



the same place. A vessel bound from Europe to America would pass 

 through a succession of heavy gales, while a powerful steamer homeward 

 bound might outstrip the gale, or remain involved for days in one storm 

 system. 



(115.) " We are, then, in possession of facts to prove that between the 

 latitudes of 35° and 50° of both hemispheres the air commonly moves to 

 the Eastward in a series of gales or systems of wind, which commence 

 with an equatorial wind, increasing temperature, and decreasing pressure; 

 that during a heavy shower of rain, when the pressure is at its lowest, the 

 wind shifts suddenly to a Westerly or even more polar direction, accom- 

 panied by a sudden increase of pressure and decrease of temperature, and 

 commonly followed by finer weather. This is 'so thoroughly understood 

 by experienced seamen, that when the pressure is decreasing fast, with an 

 equatorial wind, and a heavy shower of rain comes on, accompanied fre- 

 quently by a lull in the wind, they prepare for the sudden shift of wind, 

 which generally comes in a gust. 



" It seems probable that these systems of wind, which have such regular 

 habits, are waves of air rolling along to the N.E. in the Northern, and to 

 the S.E. in the Southern Hemisphere ; that in their front the warm air is 

 rising, and losing part of its moisture and weight by condensation, until a 

 chmax of low pressure comes, which is immediately followed by a downward 

 rush of cold air, forming a West or N.W. wind, causing the heavy shower 

 of rain or hail when it first comes in contact with the lower warm air ; also 

 an increasing pressure and decreasing temperature. 



" The North-Easterly direction taken by these waves, would most likely 

 be due to the existence of a lower pressure over the Northern part of the 

 Atlantic than over the land to the Eastward of it ; whereas the changes 

 of wind from South by the West to N.W. would be due to the internal 

 action of the wave as it sweeps along ; a section of the wave would 

 represent a kind of revolving motion in the air, with its lower edge press- 

 ing on the earth's surface, whilst its upper edge is well inclined towards 

 the Pole. 



" Professor Buys-Ballot says : — ' It is certain that, if after an unfavour- 

 able condition of pressure a S.W. wind has set in, which has veered with 

 stormy weather towards N.W., we find that generally a very unfavourable 

 condition, and usually the greatest difference, wiU be observed next day, 

 without being followed by fresh wind.' May not this be because part of 

 the North- Westerly wind is a downward motion instead of its being 

 horizontal ? 



" During Captain Martyn's outward passages (to which reference has been 

 made in (108) ) he had a decreasing pressure with a Southerly wind, and 

 an increasing pressure with a Westerly and North- Westerly wind, show- 

 ing that he was meeting gales ; whilst during his homeward passages he 

 had the pressure and wind steady for days together, showing that he was 

 either moving to the Eastward about as fast as the gale, or steaming faster 

 than the gale was moving, and had a decreasing pressure with a Northerly 

 wind, and an increasing pressure with a Southerly wind, caused by his 

 entering these systems of wind on the opposite side to what he did on the 

 passage out. 



