JOURNAL OF CHEMICAL EDUCATION
.376 mold "substsnce" is ~pplical,leneither in its usual meaning in chcmistry and other sciences nor in its strict philosophical mcaning. Snrll's law (of refraction) is introduced as a Law of Nature, vithin the context of the rectilinear propagation of light, which is a Principle. Laws of nature require careful statements of the conditions unrlet. which they are spplieahle, such as in this case, "in the alwmec of t,
