Thus we went on for a considerable distance, when suddenly a draught of cold air blew out the Professor’s light. At the same time Mr Cracker’s foot hit against some soft elastic substance of an unknowable kind, and directly afterwards he received a fearful blow upon his abdomen from something unseen. Turning round for escaping the invisible enemy, he received another blow that sent him flying heels over head, overturning the Rev. Stiffbone, who in his turn upset Mr Scalawag. They were all lying in a heap, and I heard Cracker’s voice producing a series of most unearthly yells; but the Rev. Stiffbone, while begging for mercy and blindly grasping about, clutched the air and got hold of Mr Scalawag’s hair, who defended himself with his fists; but my observations were also cut short, for I had just time, as my eyes became accustomed to the darkness, to see a still darker object rushing at me over the prostrate forms of my friends, when I myself received a severe blow upon my stomach, that caused me to lose my senses, and for a moment I knew nothing more. [Illustration: THE GROTTO OF THE NYMPHS] III. WITHIN THE UNTERSBERG. It seems that during the consternation caused by this event, I must have unconsciously wandered off, for when I gathered my senses again, I found myself in a strange labyrinth of rocks. In vain I tried to find my way back to the Dragon’s Den; there were perpendicular walls and precipices encompassing me on all sides, and the only outlet which I discovered led me still higher up towards the main body of the Untersberg. The storm-clouds had disappeared and the sky was clear; but my mind (if there is such a thing) was somewhat confused; I did not know which was which. Owing to Professor Cracker’s exposition about the unreliability of direct vision, I could not tell whether the things around me were actually there, or whether they were merely the products of auto-suggestion, trumpery, etc. More than once I bumped my head against a projecting rock, because my method of observation was not scientifically trained enough to enable me to realise the actuality of the rock without a knock-down argument. I had always fancied before that if one receives an impression from an object, be it in the waking state or in a dream, an object or image of some kind must be actually present, from which that impression comes; but now I saw that, according to science, impressions may come from nothing and may be only the products of the accidental friction of brain molecules. I was therefore no longer sure of the existence of anything that had not been analysed and attested to by a scientific expert.