278 



INDEX OF REFRACTION AND VELOCITY [Ch. 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 



1-334 



In terms of the angle of the light, if the 



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

 length in water would be 



Fig. 158. 



Fig. 159. 



Fig. 158. Critical Angle for Light Passing prom Water to 

 Aer, the Angle in Air Being 90°. 



N Normal to the refracting surface. 

 sinj. In this case sin 48° 4S' cr o.75i9 ^ J__ j^ accordance with the general 

 5(-,( ;. In this case ii» 90 or i. 0000 1.33 



formula: 



index r 



stn r index i 



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

 surface of the water. 



d d' 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 por Light Passdtg from Glass to 

 Air, the Angle in Air Being 90°. 



N Normal to the refracting surface. 

 sini In this case sin 41° + or 0.65789 ^^ ;„ accordance with the general 

 ^j„ ^ In this case ii» 90 or j, 0000 1.52 



c , sin i index r 



formula: = ; 



sin r tndex t 



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

 surface of the glass. 



d d' 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). 



