mill-on-the-floss

Tom had never found any difficulty in discerning a pointer from a setter, when once he had been told the distinction, and his perceptive powers were not at all deficient. I fancy they were quite as strong as those of the Rev. Mr Stelling; for Tom could predict with accuracy what number of horses were cantering behind him, he could throw a stone right into the centre of a given ripple, he could guess to a fraction how many lengths of his stick it would take to reach across the playground, and could draw almost perfect squares on his slate without any measurement. But Mr Stelling took no note of those things: he only observed that Tom's faculties failed him before the abstractions hideously symbolized to him in the pages of the Eton Grammar, and that he was in a state bordering on idiocy with regard to the demonstration that two given triangles must be equal - though he could discern with great promptitude and certainty the fact that they were equal.