Others (in addition to some already mentioned) are medicinal; as the palms, calabash, manchineel, pepper, fustic and a long list of cathartics, caustics, emetics, astringents, febrifuges, vermifuges, diuretics and tonics.
The investigation of caustics, being based on the assumption 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 it attracted the attention of the mathematicians of the 17th and succeeding centuries, more notably John Bernoulli, G.
1 AQP be the reflecting circle Caustics having C as centre, P the luminous point, and PQ any incident ray, and we join CQ, it follows, by the law of the b efiection.
Secondary caustics are orthotomic curves having the reflected or refracted rays as normals, and consequently the proper caustic curve, being the envelope of the normals, is their evolute.
It may be shown geometrically that the secondary Caustics caustic, if the second by refrac- medium be less refrac- tion.
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