“We had driven up in a dogcart, and my client led me away at once, without our entering the house, to the scar on the lawn where the elm had stood. It was nearly midway between the oak and the house. My investigation seemed to be progressing.

“ ‘I suppose it is impossible to find out how high the elm was?’ I asked.

“ ‘I can give you it at once. It was sixty-four feet.’

“ ‘How do you come to know it?’ I asked, in surprise.

“ ‘When my old tutor used to give me an exercise in trigonometry, it always took the shape of measuring heights. When I was a lad I worked out every tree and building in the estate.’

“This was an unexpected piece of luck. My data were coming more quickly than I could have reasonably hoped.

“ ‘Tell me,’ I asked, ‘did your butler ever ask you such a question?’