CAUSTIC. That which burns (Gr. Kav rrtcOs, burning). In surgery, the term given to substances which destroy living tissues and so inhibit the action of organic poisons, as in bites, malignant disease and gangrenous processes. Such caustic substances include silver nitrate (Lunar caustic), Potassium and Sodium Hydrates (the Caustic Alkalis) (see ALKALI), Zinc chloride, an acid solu tion of mercuric nitrate, and pure carbolic acid (Phenol).
In mathematics, the "Caustic Surfaces" of a given surface are the envelopes of the normals to the surface, or the loci of its cen tres of curvature.
In optics (geometrical optics) the term "Caustic" is applied to the envelope of luminous rays after reflection or refraction. In the first case the envelope is termed a in the second a dia-caustic. Cata-caustics are to be observed as bright curves when light is allowed to fall on a polished cylindrical surface as a napkin ring or a curved polished riband of steel placed on a table. By varying the curvature of the riband of steel or moving the source of light a variety of patterns can be obtained. The investigation of caustics, based as it is on the assumption of the law of the rectilinear propagation of light and the validity of the experimental laws of reflection and refraction, is essentially of a geometrical nature, and as such attracted the attention of mathematicians of the 17th and succeeding centuries, more not ably John Bernoulli, G. F. de 1'Hopital, E. W. Tschirnhausen and Louis Carre.
See Arthur Cayley's Memoirs on Caustics in Phil. Trans. for i857 and 1867.