The novels and stories about Sherlock Holmes by Arthur Conan Doyle are filled with keen observations of the world around him. I have read Sherlock Holmes repeatedly since I was a kid. Today, I find that Sherlock Holmes stories help me focus my own writing on details and precise observations. Recently, in reading Holmes once again, I was struck by how often there are discussions of trees, usually in passing but sometimes central to the story. In reading The Musgrave Ritual, I found this striking use of trigonometry for the measurement of trees, and it reminded my of all my friends in the Native Tree Society who are devotees of measuring trees. Here is the passage from The Musgrave Ritual:
“It was perfectly obvious to me, on reading the ritual, that the measurements must refer to some spot to which the rest of the document alluded, and that if we could find that spot, we should be in a fair way towards finding what the secret was which the old Musgraves had thought it necessary to embalm in so curious a fashion. There were two guides given us to start with, an oak and an elm. As to the oak there could be no question at all. Right in front of the house, upon the left-hand side of the drive, there stood a patriarch among oaks, one of the most magnificent trees that I have ever seen.
“‘That was there when you ritual was drawn up,’ said I, as we drove past it.
“‘It was there at the Norman Conquest in all probability,’ he answered. ‘It has a girth of twenty-three feet.’
“‘Have you any old elms?’ I asked.
“‘There used to be a very old one over yonder but it was struck by lightning ten years ago, and we cut down the stump,’
“‘You can see where it used to be?’
“‘There are no other elms?’
“‘No old ones, but plenty of beeches.’
“‘I should like to see where it grew.’
“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?’
“Reginald Musgrave looked at me in astonishment. ‘Now that you call it to my mind,’ he answered, ‘Brunton did ask me about the height of the tree some months ago, in connection with some little argument with the groom,’
“This was excellent news, Watson, for it showed me that I was on the right road. I looked up at the sun. It was low in the heavens, and I calculated that in less than an hour it would lie just above the topmost branches of the old oak. One condition mentioned in the Ritual would then be fulfilled. And the shadow of the elm must mean the farther end of the shadow, otherwise the trunk would have been chosen as the guide. I had, then, to find where the far end of the shadow would fall when the sun was just clear of the oak.”
“That must have been difficult, Holmes, when the elm was no longer there.”
“Well, at least I knew that if Brunton could do it, I could also. Besides, there was no real difficulty. I went with Musgrave to his study and whittled myself this peg, to which I tied this long string with a knot at each yard. Then I took two lengths of a fishing-rod, which came to just six feet, and I went back with my client to where the elm had been. The sun was just grazing the top of the oak. I fastened the rod on end, marked out the direction of the shadow, and measured it. It was nine feet in length.
“Of course the calculation now was a simple one. If a rod of six feet threw a shadow of nine, a tree of sixty-four feet would throw one of ninety-six, and the line of the one would of course the line of the other. I measured out the distance, which brought me almost to the wall of the house, and I thrust a peg into the spot. You can imagine my exultation, Watson, when within two inches of my peg I saw a conical depression in the ground. I knew that it was the mark made by Brunton in his measurements, and that I was still upon his trail.