CHAPTER OF VARIETIES. 185 



called Kidbrook. As I could not find any nest upon the field side of 

 the hedge I went round to the opposite side, and walking along by the 

 sandy margin of the brook tried to discover it. I crept slowly along 

 upon tip-toe, and was nearly opposite the place at which I expected to 

 find it, when suddenly I was surprised by a flight of swallows rising up 

 into the air close from the place where I was standing. When dis- 

 turbed, they seemed quite lost in confusion, and uttering a sharp plain- 

 tive cry, they dispersed in various directions, perhaps owing to the 

 darkness of the evening preventing them from collecting together, and 

 did not fly high up into the air, but, on the contrary, so low that they 

 swept the grass. Being interested in this occurrence, I went on the 

 following day and examined the place from which they arose, and found 

 that there was a long hollow fissure running under the bank, in which no 

 doubt they were secreted, and most likely were clinging to its sjdes and 

 asleep when I came up and disturbed them. However, after that evening, 

 I never saw one of them at that spot either flying in or out, from which 

 circumstance I think I am warranted in concluding that they were just 

 arrived in this country, and were resting from their fatigues, previous 

 to their repairing to their respective stations. SOLIVARIUS. 



THEORY OF RAIN. The commonly received opinion, I believe, is, 

 that the water which evaporates from the surface of the earth is held 

 in a state of chemical solution in the air, which ascends into higher 

 regions, where the moisture is precipitated in the form of clouds, which 

 are sustained there by the joint agency of heat and electricity, and 

 the deposition of rain is the result of the electrical action of the clouds 

 upon each other. 



The atmosphere, at the elevation of a few hundred yards, is at a 

 tolerably uniform temperature with that near the surface of the ground, 

 and therefore the condensation of the evaporated moisture must take 

 place at a considerable height; in tropical countries this conden- 

 sation in the form of clouds is not so frequently witnessed as in our 

 colder climate, where the temperature of the air is continually subject 

 to variation. 



That evaporation does take place at all temperatures, when the air 

 is tolerably dry, may be easily shown, by placing a cup on the surface 

 of water, containing dried potash, or fused chloride of calcium ; either 

 of these substances will deliquesce with great rapidity, or if concen- 

 trated sulphuric acid be substituted it will speedily absorb nearly half 

 its bulk of water ; the vapour which appears to rise from water and 



