The adventure of the distant blackboard

to A.C.Doyle, an ever helpful gentleman if you wish to develop a penchant for nested quotations

Mr. Sherlock Holmes, of whom I have retained a considerable number of written accounts, possessed a highly underestimated talent for coming up with the most timely and illuminating witticisms. I admit that I might be the one to blame for not reporting those to the general public, but it should be understood that the modesty of Mr. Holmes and the relentless zeal that he works with have conspired with the circumstances, allowing only the occasional pun to reach the reader interested in studying his most singular character.
It was on one of those bright sunny days that this talent was revealed. Holmes and I were sitting on a large branch, having just climbed an old and respectable tree - he with the agility which was hard to deduce at first glance from his thin long physique and me with some difficulty, aided by the determination of a disciple willing to get to the bottom of his master's obscure narrations.
As I was catching my breath and re-tying my shoe-laces, Holmes took a large military binocular from one of his pockets and the most unsavoury of his smoking pipes from another. So consumed he was by his investigation that for a moment there I fancied he would bring a match to the binocular and start puffing on the narrow end. Fortunately, though, it was the tobacco in his pipe that he managed to ignite after a few false tries.
"Tell me, Watson, what do you see?" he inquired.
Having by that time learned the importance of an outside eye and the great assistance it can be to my friend, I endeavoured to observe the scene and make inferences, mimicking him as best I could.
"I can see a window, quite large, no shuts, nor are the curtains obscuring our view, not at the moment, anyway," I started to report when I considered that I have observed all I could. "Inside there's a cabinet, rather spartanly decorated, if I may say so. Besides a large and possibly comfortable wooden desk I can see a blackboard, upon which a very tall gentleman is working out a problem."
"Do you recognise the gentleman?" Holmes asked. He was evidently so eager to see whether I was acquainted with the man that he took the binocular away from his eyes for a moment and turned to me with a most penetrating gaze.
"I cannot say that I do," I replied, for that was the case.
"Well, it can be argued that nor should you. Let me introduce you, then." Holmes returned to watching the gentleman intently via his optical contraption, while I continued the same observation without such aid. The man in the cabinet was using a right angle and appeared to be plotting a co-ordinate plane. While he was plotting, Holmes was explaining, "The person you see in this cabinet is none other than Professor Moriarty. The whole story of his life would regrettably have to wait for some other time, but for now suffice it to say that he is the singular most dangerous criminal in all England and quite possibly all Europe as well. I've been fascinated by his methods and his ambitions for quite some time now, Watson, and have been following him and watching him on numerous occasions, although few were quite as dramatic as this one, and I dare say - "
The professor's hand was poised over the board for a moment, and then in one calculated snake-like stroke he added a final touch to the figure he was drawing.
"I rather see his point."