Notwithstanding that so much of Abernethy's lecturing was on anatomy, and therefore necessarily addressed to the eye, yet he seldom offered any _illustration_ to the external senses. He was always endeavouring to impress the mechanical arrangement of parts, by reference to their uses and surgical relations. Even in speaking of light, he would be suggestive beyond the mere perception of sense. He used to say, of refraction of light, when the refracting medium was, as it commonly is, the denser body, "that the ray seems as if attracted"—a very suggestive phrase to any one who has thought much on the subject of light. It is a curious thing to observe how confused the ideas of many people are on phenomena of light; and we are afraid that the cause is, that the illustrations to the eye are given _too soon_. If people were made to _understand_ by a simple illustration what they are about to _see_, it is probable they would have much clearer ideas. The intellect having gone before, the eye no longer diverts it from its office; and the eye would then be merely _impressing_, by means of a physical representation, an established idea. [Footnote 67: Vol. i, p. 23.] CHAPTER XXIII. "Suavis autem est et vehementer sæpe utilis jocus et facetiæ."—CIC. DE ORAT. Abernethy's humour was very peculiar; and though there was of course something in the matter, there was a good deal more, as it appeared to us, in the manner. The secret of humour, we apprehend, lies in the juxtaposition, either expressed or implied, of incongruities, and it is not easy to conceive anything humourous which does not involve these conditions. We have sometimes thought there was just this difference in the humour of Abernethy, as contrasted with that of Sidney Smith. In Smith's, there was something that, told by whom it might be, was always ludicrous. Abernethy's generally lay in the telling. "The jest's propriety lies in the ear Of him who hears it, never in the tongue Of him that makes it," although true, was still to be taken in rather a different sense from that in which it is usually received. The former (a far higher species of humour) may be recorded; the dramatic necessities of the other occasion it to die with the author. The expression Abernethy threw into his humour (though of course without that broadness which is excusable in the drama, but which would have been out of place in a philosophical discourse) was a quiet, much-subdued colouring, between the good-nature of Dowton, and (a little closer perhaps to the latter) the more quiet and gentlemanly portions of Munden. Few old pupils will forget the story of the Major who had dislocated his jaw.