M. @. Lea on certain phenomena of Light. 369 
pended in the liquid, If this be then placed in a glass trough 
_ with parallel sides, and a beam of sunlight be sent through it 
and received on a screen 15 to 20 feet distant, the image has 
a deep yellow color. The liquid itself presents a rich blue 
tint. If the liquid be transferred to a large glass vessel with 
cut facets placed in direct sunlight, the effect is very beautiful, 
flashes of deep gold colored light contrast finely with the rich 
blue of the liquid. 
Case third. —Blue light and red are seen simultaneously and 
both are diffused, 
If we take the index of refraction of the glass at 15 it is | 
evident that the ray passing through the natural surface will 
be retarded in the proportion of 1'5 to 1 for a distance equal - 
