M, C. Lea on certain phenomena of Light. 371 
them. As the reflecting surfaces will be irregularly distributed 
in every direction, the light which is not transmitted will be 
reflected in every direction. This diffusely reflected light will 
in some cases pass through the particles, in other cases 
between them. If the particles have a higher index of po dae 
tion, those rays that pass through them will be retarded; if a 
lower index, they will be accelerated. In either case, those 
that pass through the edges of the particles will be in a condi- 
tion to interfere with those that pass immediately adjacent, 
And if the particles be very small, the number of such inter- 
ferences will be very great, and the preponderance of color pro- 
duced will be red by the extinction of blue rays, 
Nor is this the only way in which interference may take 
place. If we suppose the two bounding planes of the particles 
through which the ray passes, to be parallel or nearly so, it 1s 
evident that interference may result between the transmitted 
tay, and another ray twice reflected in the interior of the 
particle precisely as in the case of the plate of air, etc., in 
Newton’s thin plates. i 
_ This latter mode of interference also gives us easily the key 
to the production of blue diffused color in the second and 
third cases. 
mM some cases with nearly perpendicular incidence upon parti- 
necessary for the red, and the reflected ray will be tinged 
with blue. ee 
_If the particles have a greater index of refraction than the 
on 
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um, the Tay rt 2a a 
