192 



DR. BREWSTER ON REFLECTED LIGHT. 



is particularly fine, and the whole phsenomenon is one of the most beautiful in 

 physical optics. 



When the incident light is homogeneous, no colours of course are seen ; 

 but the reflected pencils have their maxima and minima of intensity, like the 

 rings of thin plates or the fringes of inflected light when formed by homoge- 

 neous rays. 



The following are the periods for red and for blue light. 



Ked Light. Blue Light. 



1st minimum ... 77 54 ... 80 27 

 2nd minimum ... 50 57 ... 59 4 



If we substitute for the prism A a square prism, the tints are thrown more 

 closely together ; and if the luminous object is a long stripe of bright light, we 

 may see most of the colours at one view. 



If we now apply heat to the oil so as to diminish its refractive power, the 

 brightness of the colours is greatly diminished, and the first period is com- 

 pleted at a less angle of incidence. 



Such are the phaenomena which take place when the refractive power of the 

 glass exceeds that of the fluid. We shall now see what happens when the 

 fluid has a greater refractive energy than the solid ; a case of peculiar interest, 

 because we are able to reduce the two refractive powers to a perfect equality 

 for any given ray of the spectrum. 



The same prisms being employed, let the film C D H G be now balsam of 

 capivi. Before total reflection takes place, the reflected pencil is perfectly 

 white : it then becomes yellow, and passes through the same orders of colours 

 as in castor oil. All the colours, however, are produced at less angles of in- 

 cidence, the 1st order terminating at an angle of 64° 58', as appears from the 

 following Table, in which I have given only the leading tints. 



Angles of Incidence 

 Angles of Incidence on the Surface 



BrE. 



o 



Colours. 



^Yellowish 47 



Yellow , . 41 



1st Order.< Pink red 36 



Pink 33 



LLimit of pink and blue 31 



CoD. 



O f 



74 10 



70 47 



67 57 



66 10 



64 58 



