VESICLES OF FOG. 283 



warmer current takes place, that its excess of 

 moisture is immediately rendered visible as 

 fog, and is rapidly deposited. There has been 

 much question in the minds of the learned, as 

 to the exact nature of this phenomenon. The 

 greatest number of philosophers believe the 

 watery particles to be vesicular, or like so many 

 minute hollow spheres of water ; in fact, like 

 miniature soap-bubbles. These vesicles are 

 supposed to have repulsive tendencies towards 

 one another. M. de Saussure, who paid more 

 than ordinary attention to this subject, saw in 

 fogs which he examined on the Alps, vesicles 

 float before him as large as peas, the coating of 

 which was inconceivably thin. This view has 

 been recently doubted, and in a communication 

 read before the Eoyal Society, Dr. Waller has 

 attempted to prove that the watery particles of 

 fog are not vesicular, but are minute spherules, 

 or solid beads of water alone. Fog is probably 

 composed both of vesicular and solid particles of 

 water. 



Whatever be their physical constitution, a 

 large aggregate of such particles in the higher 

 regions of the air produces the phenomenon of 

 Clouds. All that exquisite and inexhaustible 

 variety of effect, which the artist loves to 

 imitate, and the eye to rest upon ; all those 

 glowing pictures of mansions in the skies, of 



