It is an amazing story, and full of tantalising hints as to what might be in the great ascetic’s own account. But nowhere could I find any reference to the original, not even in Duncan’s own papers. Then, while trying to identify a mountain mentioned in Duncan’s article, Google took me to a piece in the European Magazine from 1810 which turned out to be Pūrṇ Purī’s own account! I don’t think any modern scholars have noticed it - it is certainly not cited in any of the secondary sources I’ve consulted. As well as being the travel story to end all travel stories told by a sympathetic and funny narrator, it is full of all sorts of fascinating incidental information, including more grist to the mill of my thesis that tapas is the main source of non-seated āsana practice. PP lists the 18 tapasyās (which as far as I know are not found elsewhere) and number 8 is caurasi āsan, i.e. the 84 āsanas, “difficult postures in sitting, such as continuing several hours with the feet on the neck or under the arms; after which the members are returned to their natural positions” (pp. 263-264). He makes no mention of yoga anywhere.
Then, after making me establish my credentials with a demonstration of my finest āsanas, Anūp Nāth Jī proceeded to smoke a chillum and show me an amazing sequence of poses marred only by a rather grating “dance” soundtrack. I was surprised, not least because I had thought that there were very few āsana practitioners among the Nāths. When I asked him where he had learnt his practice, he said it had come to him apne-āp, “automatically”, when he was a boy. Apologies for the poor quality - the lighting was low and the camera a point-and-shoot compact.