REFRACTION. 



97 



For instance, a straight stick when plunged into water appears to be 

 broken at the point of immersion. This appearance is caused by the rays 

 of light taking a different direction to our eyes. 

 If in the diagram (fig. 89) our eye were at o, and 

 the vessel were empty, we should not see m ; but 

 when water is poured into the vessel the object 



will appear higher up at n, and all objects under v \ 

 water appear higher than they really are. 



One may also place a piece of money at the 

 bottom of a basin, and then stoop down gradually, F >g- 8 9 . Refraction in water, 

 until, the edge of the basin intervening, the coin is lost to view. If an 

 operator then fills the basin with water, the piece of money appears as 



Ffg. 90. A water-bottle employed as a convergent lens. 



though the bottom had been raised. The glass lenses used by professors 

 may be very well replaced by a round water-bottle full of water. A candle 

 is lighted in the darkness, and on holding the bottle between the light and 

 a wall which acts as a screen, we see the reflected light turned upside down 

 by means of the convergent lens we have improvised (fig. 90). A balloon 

 of glass constitutes an excellent microscope. It must be filled with per- 

 fectly clear, limpid water, and closed by means of a cork. A piece of wire is 

 then rolled round its neck, and one end is raised, and turned up towards the 

 focus ; viz., to support the object we wish to examine, which is magnified 

 several diameters. If a fly, for instance, is at the end of the wire, we find 

 it is highly magnified when seen through the glass balloon (fig. 91). By 

 examining the insect through the water in the balloon, we can distinguish 

 every feature of its organism, thanks to this improvised magnifier. This 



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