ECHO. 



525 



we know the origin of the sharp, piercing "ping" of the Gnat, 

 and the heavy, dull boom of the Hunihle-bee, both of which 

 insects are given in the illustration. 



Before taking leave of this subject, I may mention that the 

 instrument is called the Siren because it sings as well under 

 water as in the air, provided that water instead of air be 

 driven through it. 



ECHO. 



OUR last page will be given to the phenomenon called by the 

 name of ECHO, which consists in the power of solid substances, 

 whether natural or artificial, of reflecting the waves of sound 

 thrown against them, just as a mirror reflects the waves of 

 light. 



Very often the Echo is naturally formed, as shown in 

 the illustration, by rocks which cast back the sound waves 

 thrown against them. This is the case in several parts of 



WHHPKBING (JALLKBY. 



Dovedale in Derbyshire, where a pistol shot is reverberated 

 backwards and forwards in a most wonderful manner, and a 

 trumpet blast repeats itself over and over again. 



At Walton Hall, the residence of the late C. Waterton, Esq., 

 there is a wonderful Echo, nearly half a mile from the house. 

 Mr. Waterton had discovered the Echo, which proceeded from 

 the walls of the house, and, having found its focus, placed on 



