2 7 8 



INDEX OF REFRACTION AND VELOCITY [Cn. IX 



waves at the D Fraunhofer line (Watson). This means that if 

 the speed in the ether were i, that in water for this wave length the 



velocity would be 



In terms of the angle of the light, if the 



1-334 

 sine of the angle in the ether is i, the sine of the angle of this wave 



i 



length in water would be 



1-334 



FIG. 159. 



FIG. 158. 



FIG. 158. CRITICAL ANGLE FOR LIGHT PASSING FROM WATER TO 

 AIR, THE ANGLE IN AIR BEING 90. 



N Normal to the refracting surface. 



sini In this case sin 4 f 45' or 0.7510 = _i_ in accordance with the general 

 S i n r In this case sin 90 or I>0000 I>33 ' 



formula: 1 = i -^- r 

 sin r index i 



b Light ray at the critical angle and emerging into the air parallel with the 

 surface of the water. 



d d r Ray of light at an angle greater than the critical one and being internally 

 reflected back into the water; the angle of incidence and reflection being equal 

 (fig. 152). 



FIG. 159. CRITICAL ANGLE FOR LIGHT PASSING FROM GLASS TO 

 AIR, THE ANGLE IN AIR BEING 90. 



N Normal to the refracting surface. 



sinj. In this case sin 41 + or 0.65789 = _^_ in accor dance with the general 

 sin r In this case sin 90 or 1>oooo I<52 ' 



formula: 



sin r index i 



b Light ray at the critical angle and emerging into the a'ir parallel with the 

 surface of the glass. 



d d f Ray of light at an angle greater than the critical angle and being reflected 

 back into the glass, the angle of incidence and reflection being equal (Fig. 152). 



