EVAPORATION OF WATER. 



a collection of insects, another studied botany. In the daytime we might 

 have been seen examining, under a magnifying glass, the branch of a rose- 

 tree, from which the ants were endeavouring to extract the aphides* (fig. i). 

 At night we admired through the telescope 

 the stars and planets that were visible ; or 

 if the sky was not clear, we examined under 

 a strong magnifier grains of pollen from 

 flowers, or the infusoria in a drop of stag- 

 nant water. Frequently some very insignifi- 

 cant object became the occasion for some 

 scientific discussion, which terminated with an 

 experimental verification. 



I recollect that one day one of us 

 remarked that after a week of dry weather 

 a stream of water had nearly dried up, 

 although sheltered by thick trees, which ne- 

 cessarily impeded the calorific action of the 

 sun ; and he expressed surprise at the rapid 

 evaporation. An agriculturist among the 

 company, however, drew his attention to the 

 fact that the roots of the trees were buried 

 in the course of the stream, and that, far 

 from preventing the evaporation of the water, 

 the leaves had contributed to accelerate it. 

 As the first speaker was not convinced, the 

 agriculturist, on our return to the house, 

 prepared an experiment represented in fig. 2. 

 He placed the branch of a tree covered with 

 foliage in a U-shaped tube, the two branches 

 of unequal diameter, and filled with water. 

 He placed the vegetable stem in the water, 

 and secured it to the tube by means of a 

 cork covered with a piece of india-rubber, and 

 tied tightly to make it hermetically closed. 



At the commencement of the experi- 

 ment the water was level with A in the larger 

 branch of the tube, and level with B in the 

 smaller, rising by capillarity to a higher point 

 in the more slender of the two. The evapora- 

 tion of the water caused by the leaves was so 

 active that in a very short time we beheld the water sink to the points c and C. 



Fig. a. Experiment showing evaporation ot 

 water by leaves. 



* It is well known that ants, by touching the skin of aphides, extract therefrom 

 a secretion of viscous matter, which nourishes them. They will frequently carry off the 

 aphides to their habitations, and keep them there ; thus one may say they keep a cow in their 

 stable 



