176 WESTERN SERIES OF READERS. 



tant objects on the earth, like the trees on a moun- 

 tain side. Still smaller ones are known as opera- 

 glasses. These are not very powerful, but are 

 convenient in a large hall, when one wishes to see 

 the features of the speaker or singer more dis- 

 tinctly. But all true telescopes are used in air, 

 and never in the water. 



A water-telescope is an instrument which will 

 assist one to see objects that are underneath the 

 surface of water, particularly those that are at the 

 bottom of a lake or bay. 



If you go out in a boat, you know how hard it 

 is to see the tishes that are swimming about in 

 the water beneath you. Almost all the time there 

 is a breeze, which makes ripples on the surface of 

 the lake, and you know you cannot see clearly 

 through ripples. 



Even if there is no wind, the boat itself makes 

 little waves, and though the water is only ten feet 

 deep, it might just as well be a hundred, so far as 

 seeing the bottom is concerned. A water-tele- 

 scope destroys the ripples, and lets you look 

 through water as if it were clear glass. 



It is nothing but a box with a water-tight glass 

 bottom. If you set this box on the water, and 

 press it down a little, you will find that when you 

 look into the top, you can see through the glass, 



