It is extraordinary how many people have an obliquity in their mental vision. Some mentally never see straight at all, but look at everything askew. These are harmless people; you know them at once, and pity their defects, just as you do a person with a downright squint. But those who have a slight cast in the eye are the most dangerous; you are not aware they occasionally squint; you do not perceive, perhaps after even a close scrutiny, that there is anything amiss with their vision at all. So it is with the mental cast; you do not observe it, as a general rule, for it is only now and then it shows itself.

When the Antiquity of Man was first proclaimed from the discovery of the Abbeville flints by Boucher de Perthes, no one believed it. Everybody thought him like the mad man who swore all the world was mad; and so it seemed, then, as if all the world had mental obliquity of vision, which made them declare our savant of Abbeville to be labouring under a delusion. When, however, Rigollet, Prestwich, Flower, Lyell, Evans, and others of the goodly company of geologists,—as unbelieving, however, as so many St. Thomases,— went, saw, and returned believing, the fame of Boucher de Perthes' discoveries gained ground.