IMPURE WATER. 361 



it to be so inferior to the water of springs. When 

 allowed to stand in reservoirs, that water may let fall 

 the earthy substances that it holds mechanically sus- 

 pended ; but nothing, except filtration through a bed 

 of sand or some other substance, that can completely 

 keep back the feculent eggs or larvae that can float in 

 it, will preserve it from putrefaction if it afterwards 

 be allowed to stand for any length of time. It is the 

 same whether these animal impregnations live or die, 

 If they live they are unseemly, they prey upon each 

 other ; and whether they do or not, they leave their 

 exumce behind, when they change into the fly or imago 

 state, and sport their new wings in the air; these 

 putrefy, a decomposition takes place, some of the 

 water is decomposed, mixes with sulphur, and the 

 odour is offensive. Boiling, if the water be allowed 

 to settle afterwards, gets the better of those impurities; 

 but they are got rid of at an expense ; the water is 

 deprived of its air of that very carbonic acid with 

 which the respiration of the little things impregnated 

 it ; both its sparkle and its sharpness are gone, and 

 it is flat and insipid a vehicle merely, and not a 

 stimulant. 



Situations which abound so much with insect life 

 both on the wing and in the water, as brooks and their 

 borders, of course, supply food for numbers of insecti- 

 vorous birds. Of these, a portion are adapted for 

 wading, and preying upon their insect food in the 

 shallow water, while others course it on the wing; 

 and in both descriptions, but more especially in the 

 latter, there are some of the most extraordinary con- 

 trivances in nature. Of the waders in brooks, one of 



