ARUAN. METEOROLOGY. 329 



to have moved in an undulating plane, so as to have 

 touched the surface at the points which presented a con- 

 vexity downwards. It must indeed have often been 

 observed, that currents of air, even on shore, are curvi- 

 linear ; and thus only can we explain a circumstance by 

 no means unusual, particularly in summer, when such irre- 

 gular winds appear to be most prevalent. This is, the occur- 

 rence of a south or of a westerly wind in a particular tract, 

 when the general wind is from the east, and when that is 

 indicated, even in the particular spot where it does not 

 exist, by the peculiar well known colour and aspect of the 

 horizon and of the distant hills. There is no doubt that in 

 these cases, partial differences of temperature in the surface 

 of the earth will induce such variations, and they accord- 

 ingly vary with the time of day and the position of the sun. 

 It is equally certain that the squally winds are often 

 produced by reverberation from mountainous land, or by 

 the confinement of the current in a narrow passage ; but 

 as all the same phenomena take place in the open sea 

 where such causes do not exist, it is obvious that there 

 are also causes of a different nature still unknown to us. 



In concluding this sketch I shall add one case of a 

 still more intricate nature, and, at present, equally defying 

 our powers of explanation. 



In passing down the Clyde, and being off the point of 

 Dunoon with a south-westerly wind close hauled, a sloop 

 was observed standing up in an opposite direction, in the 

 same manner and on the same tack, each having a fresh 

 breeze. To ascertain the proximity of the two opposed 

 currents, our vessel was caused to run alongside of the 

 other and to pass within fifty yards. It was thus dis- 

 covered that there was no line of smooth water between 

 them ; whence it was evident that these opposite and 

 rapid streams of air were in contact. At some distance 

 under the Ayrshire land, the vessels were all becalmed. 

 It is evident that those which were crossing this double 

 current, must have been at the same time taken suddenly 



