192 
DR. BREWSTER ON REFLECTED LIGHT. 
is particularly fine, and the whole phaenomenon 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. 
Red Light. Blue Light. 
Of Of 
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 phenomena 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 CDHGbe 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 1 st 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 
Colours. R r E. 
Angles of Incidence 
on the Surface 
CoD. 
[“Yellowish 
0 
. . . 47 • . 
o / 
. . 74 10 
Yellow 
. . . 41 . . 
. . 70 47 
1st Orders 
Pink red 
. . . 36 . . 
. . 67 57 
Pink 
. . . 33 . . 
. . 66 10 
..Limit of pink and blue . . 
. . . 31 . . 
. . 64 58 
