Key right through these paragraphs twice.
"I wonder if you know when to use the semi-colon?" asked the teacher. "It is used when a conjunction - a 'joining word' - is omitted; when a longer pause is needed than a comma; when listing not words but short phrases."
"Yes, I did find him; but that was yesterday in Stratford-on-Avon; not in Kingston-upon-Thames. It was at ten o'clock. Then to-day I saw him again in Newcastle-under-Lyme!"