called Wind Reels, 



455 



be always referred to optical deception ; for I have, more than 

 once, observed arched clouds in various positions and direc- 



198 



?f^^^^%#^ 



tions, with regard to the eye, which they could not have ap- 

 peared in according to this supposition. 



I continued to observe and admire those arched lines of 

 cloud for several hours, namely, from noon till between four 

 and five in the evening ; and, what was remarkable, though 

 there was a light but steady breeze of wind in the direction 

 of the arched lines, the form of the cloud remained nearly 

 stationary, and uniform in its outline. Now, are we to infer 

 from this, that a thin light stream of vapour, spread over the 

 whole extent of the horizon, and acted upon, for four or 

 five hours, by a breeze of wind, would neither be evaporated 

 nor moved from its position ? The affirmative would be the 

 natural inference ; but Mr. Daniell, in his excellent Essays on 

 Meteorology, has endeavoured to account for the apparent sta- 

 tionary phenomena of clouds, in so very ingenious and satis- 

 •factory a manner, that I hesitate not to adopt his explanation. 



" The apparent permanency," says Mr. Daniell, " and 

 stationary aspect of a cloud, is often an optical deception, aris- 

 ing from the solution of moisture on one side of a given point, 

 as it is precipitated on the other. No phenomenon is more 

 common amongst mountains, or upon hills by the sea -side, 

 than clouds upon the summits, which appear to be perfectly 

 immovable, although a strong wind is blowing upon them at 

 the time. That this should be the real state of the case, is 

 clearly impossible, as so attenuated a body as constitutes the 

 substances of the clouds must obey the impulse of the air. 



