quite literally
Many a strange phrase strays about third-rate fiction to puzzle literal-minded readers. There is, for example, a remark often made, he wiped his glasses. This means that he felt emotion, and the implication is that the moisture which rose to the eyes in consequence of the emotion had settled on and dimmed the glasses. But I am informed by those who wear glasses that this is not what actually occurs, and that, when tears gather in the eyes, they do not spray out horizontally so as to wet the glasses, but either remain in the eyes unfallen until reabsorbed, or roll vertically down the cheeks; nor do they give out steam or mist; therefore this process of wiping the glasses is not called for more at lachrymose moments than at others. If this is, as seems probable enough, the case, then either those who use this phrase do not know it, or, knowing it, they ignore it, and deliberately use the words he wiped his glasses as a convenient (because indirect) way of saying ‘tears were in his eyes.’
Since Macaulay assures us the fiction in question is third-rate, perhaps I should not suggest that she is, in this passage, psychologically obtuse. So: tears, in ordinary circumstances, do not dampen glasses – agreed. He does not, therefore, need to ‘wipe his glasses’ – fair enough. A question: in moments of distress how many people do only what they need to do? No one, in order to distract himself and draw attention away from his emotional state, would cough when his throat does not need clearing, nor would he, say, remove his glasses (thus taking an opportunity to look down and hide his face) and ‘clean’ them? Not in third-rate fiction, of course; there a spade is always an implement used in the course of cultivation for the purpose of upturning earth; but a snob is still a snob.