1. The _British Quarterly_ Reviewer quoted for my instruction the _dictum_ of Professor Tait, that “Natural Philosophy is an experimental, and not an intuitive science. No _à priori_ reasoning can conduct us demonstratively to a single physical truth.” Thereupon I inquired what Professor Tait meant “by speaking of ‘physical _axioms_,’ and by saying that the cultured are enabled ‘to see _at once_ their _necessary_ truth?’” . . . No reply. 2. Instead of an answer to the question, how this intuition of necessity can be alleged by Professor Tait consistently with his other doctrine, the Reviewer quotes, as though it disposed of my question, Professor Tait’s statement that “as the properties of matter might have been such as to render a totally different set of laws axiomatic, _these laws_ [of motion] _must be considered as resting_ _on convictions drawn from observation_ _and experiment, and not on intuitive_ _perception._” Whereupon I inquired how Professor Tait knows that “the properties of matter _might have been_” other {316} than they are. I asked how it happened that his intuition concerning things _as they are not_, is so certain that, by inference from it, he discredits our intuitions concerning things _as they_ _are_ . . . No reply: Professor Tait told, _à propos_ of my question, a story of which no one could discover the application; but, otherwise, declined to answer. Nor was any answer given by his disciple.