  This short note revisits a classical result that the complete caustic by
refraction of a circle is the evolute of a Cartesian oval. We provide
additional details to the statement and geometric proof of this fact, as
presented in G. Salmon's 1879 book `Higher Plane Curves'. We observe that as
the circle tends to a line, this Cartesian oval collapses into an ellipse.
Finally, we discuss a computational method to find the complete caustics by
refraction, independent of Salmon's proof.
