522 



tached with difficulty. The air-plate' all over the surface must thus 

 become continually renewed and the arrangement kept perfect. 



Sensible respiration is not at all essential to the repelling power of 

 leaves ; the most beautiful manifestation of it I have met with is in 

 the Pestia, a little floating water-plant abounding in our shallow 

 tanks, and resembling common endive. When pushed under the 

 surface, it looks like a little mass of burning silver. The same ap- 

 pearance is presented on cabbages, young clover, and a vast variety 

 of other leaves ; it is the cause of the bright pearl-lustre of dew. 

 The same phenomenon is manifested on the wings and backs of divers 

 when they dash into the water. In this case it has been ascribed, 

 most erroneously as I believe, to the presence of grease or oil in the 

 feathers, and is, I have no doubt, due to the presence of an air-plate 

 repelling the water, so that it never comes in contact with the feathers 

 at all. The trimming process, so carefully performed by Water 

 Fowl, is probably an application of oil or grease, with the object of 

 separating or dressing the little fibres of the feathers so as to produce 

 an arrangement fitted to entangle the air. The reflexion of light 

 from the lower surface of the water is the proof of want of contact. 

 A piece of polished marble or of glass, a waxed, oiled or greased 

 surface, readily throws off the water without remaining wetted ; but 

 no reflexion is in this case observable. 



Might not the manufacturers of waterproof cloth or clothes take a 

 hint on this point from the economy of nature ? Could they ma- 

 nage to produce a surface such as would entangle and retain a film of 

 air, no india-rubber varnish or other water-tight material would 

 be required, while the texture would permit the free transmission 

 of respiration or moisture from the body, which Mackintosh's and 

 other similar contrivances obstruct. 



