THE EEA.SON WHY. 



And God said, Let the waters under the heaven be gathered together unto ona 

 place, and let the dry land appear : and it was so." GEX. i. 



Because there are various reflecting surfaces, at different 

 distances, each of which returns an echo. 



746. Are sounds reflected only by distant objects ? 

 Sounds are doubtless reflected by walls and ceilings around 



us. But we do not perceive the echoes, because they are so near 

 that they occur at the same moment with the sound. In lofty 

 buildings, however, there is frequently a double sound, making the 

 utterance of a speaker indistinct. This arises from the echo follow- 

 ing very closely upon the sound. 



747. Why, when we are walking under an arch-way or a 

 tunnel, do our voices appear louder ? 



Because the sounds of our voices are immediately reflected. And 

 as a gas reflector increases the intensity of lirjJit, so a sound 

 reflector will increase the apparent strength of our voices. 



There are many places where remarkable echoes occur. On the banks of the 

 Rhine, at Lurlcy, if the weather be favourable, the report of a rifle, or the sound 

 of a trumpet, will be repeated at different periods, and with various degrees of 

 strength, from crag to crap, on opposite sides of the river alternately. A similar 

 effect is heard in the neighbourhood of some of the Lochs in Scotland. There 

 is a place at Woodstock, in Gloucestershire, which is said to echo a sound fifty 

 times. Near Rosneath, a few miles from Glasgow, there is a spot where, if a 

 person plays abar of music upon a bugle, the notes will be repeated by an echo, 

 but a third lower; after a short pause, another echo is heard, again in a lower 

 tone ; then follows another pause, and a third repetition follows in a still lower 

 key. The effect is very enchanting. The whispering galleries of St. Paul's, of 

 the cathedral church of Gloucester, and of the Observatory of Paris, owe their 

 curious effects to those laws of the reflection of sound, by which echoes are pro- 

 duced ; but in these cases the effect is assisted by the elliptical form of the 

 edifice, each person bemg in the focus of an ellipse. 



CHAPTER XXXV, 



748. What is water? 



Water is a fluid composed of two volumes of hydrogen to one of 

 oxygen, or eight parts by weight of oxygen to one of hydrogen, 

 It is nearly colourless and transparent. 



749. Why, if a saucer of water be exposed to the air, mil 

 it gradually disappear ? 



