"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 knowing 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 your 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 23 ft.' "Here was one of my fixed points secured. "'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?' "'Oh, yes.' "'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 dog-cart, 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 64 ft.' "'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 on 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 further 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."