DROPPING FROM LEAVES. 35 



of any other form, whose greatest linear diameter did not exceed the 

 thickness of that central spot in a soap bubble which reflects no light, 

 would be equally non-reflective, and therefore incapable of forming a 

 rainbow. In the undulating theoiy, however, it is the parallelism of 

 the surfaces of the film of which that central spot consists which 

 renders it non-reflective. I suspect, however, that in the case con- 

 templated in the text that theory, carefully re-examined, would render 

 a somewhat difi'erent account of the singular abruptness of transition 

 from the most brilliant reflexion to an almost absolute extinction of 

 the reflected ray, and of the uniformity over large areas of a thin film 

 of the still remaining fraction of the incident light which it does 

 reflect, than that usually given." 



Of the undulatory theory of light I shall have occasion, in a sub- 

 sequent part, to treat at some length. 



Whatever may be the form of the cloud particles, be they drops or 

 bubbles, they are in the cloud or mist so far apart — and are kept 

 apart by conflicting attractions, exercised by all upon each and by 

 each upon all — that it is long before multitudes coalesce to form rain- 

 drops, and a slight rise of temperature may lead to their being again 

 absorbed by the air without their falling to the ground; but the 

 particles deposited on the leaves, brought into closer proximity, and in 

 many cases contact, rush into each other like drops of quick-silver, 

 and the attraction towards the earth becoming greater than the 

 attraction of adhesion they fall from the leaf to the ground. And 

 thus may the dropping reported have been occasioned. 



In passing through a fog the moisture collects like dew-drops on the 

 hair, the whiskers, the eye-brows, and even on the eye-lashes, and on 

 every projecting filament of wool in the clothes ; and so is it also 

 with the cloud or mist surrounding a tree, or borne through the 

 interstices of its twigs by the wind, the minute drops collect upon 

 its leaves. And I presume the fact has only to be mentioned to 

 recall to some of my readers that in a mist they have seen heavy 

 drops falling from foliage while there was no rain. 



I find some pertinent observations on this point in a work entitled 

 "The Climate and Resources of Madeira," by Dr Graham, a work- 

 which I shall afterwards again have occasion to quote. The author 

 remarks, — "The power of trees upon mist is very great. Where 

 there are no trees, the cloud drives along, depositing little or no 

 moisture. But trees largely intercept mist ; and the small component 

 vesicles of water coalesce upon the leaves and branches, and fall in 

 drops of water upon the earth. The mists form, whether there be 



