34 PHENOMENA OF VEGETATION. 



the statement of Humboldt, measuring several thousand times the 

 area of the ground they cover. And there should be as little to 

 startle one in finding dew-drops falling from a tree while the sky 

 is cloudless and serene, as in finding melted hoar-frost dropping 

 when the sun has arisen upon the tree in winter. 



But in the case of the laurel at Ferro it is expressly stated, " every 

 morning the sea breeze drove a cloud towards the wonderful tree, 

 which attracted it to its huge top." Such were the phenomena, and 

 the explanation which suggests itself is more simple. In regard to 

 fog or mist — and a cloud is only a form of this — Sir John Herscheh 

 in the treatise from which I have already quoted, says, — " The form 

 in which the moisture so precipitated first appears will necessarily be 

 that of very minutely-divided particles, which, however, having the 

 refractive power of water, reflect and refract light as such, and appear 

 therefore as a mist, fog, or cloud of greater or less density and opacity, 

 according to the amount precipitated in a given volume. It is a 

 favourite dogma with many meteorologists that the particles so pre- 

 cipitated assume the form, not of drops, but of hollow spheres or 

 bubbles. De Saussure states that he has seen such, floating before his 

 eyes in clouds and fogs on the Alps, and the dusty appearance of the 

 vapour floating over a cup of cofi'ee in the sunshine is adduced in 

 illustration. The strongest argument adduced in their favour, however 

 (for there is great room for optical illusion in such matters), is that 

 adduced by Kratzenstein, that the sun striking on a cloud or fog 

 produced no rainbow, which it ought to do were the water collected in 

 spherical drops. This argument does not admit of a ready answer ; 

 but the difficulty, on the other hand, of conceiving any possible mode 

 in which such bubbles can be formed disposes us to believe that the 

 extreme minuteness of the globules may be found to afford one, their 

 diameter being of an order comparable with the breadth of the 

 luminiferous undulation." 



Thus wrote Herschel in the article in the Encyclopaedia. To the 

 second edition of the article, published as a volume in 1861, he added 

 in one foot-note that he had never himself seen such a phenomenon as 

 was spoken of by Saussure, and that he had questioned Alpine excursion- 

 ists of far more extensive experience than his own, with a like negative 

 reply. And in a second foot-note he says, — " On the Newtonian 

 doctrine of fits of easy transmission and reflection, or (which comes to 

 the same thing) on the hypothesis of light consisting in rotating cor- 

 puscles with attractive and repulsive poles, there would be no difficulty 

 of the kind [mentioned in the text]. A globule, or a particle of water 



