The history upon which I am now embarking abounds in incidents so amazing that, as I look back on them, a something approaching to scepticism contends with my vivid recollections and makes me feel almost apologetic in laying them before the reader. Some of them indeed are so out of character with the workaday life in which they happened that they will appear almost incredible; but none is more fraught with mystery than the experience that befell me on a certain September night in the last year of my studentship and ushered in the rest of the astounding sequence.