Deeper and deeper we plunged into the mountain fastnesses. It was clear from the temperature our cooking water boiled at that we had risen to a great altitude, and Poyning and I were already troubled with height-sickness. Philipson concocted from his medicine chest a tonic that quickly reduced the fever, but we still had great difficulty in getting our breath in the rarefied air, and there was worse to come, for our route lay far higher yet. Moreover, to advance had become a matter of the utmost hardship. Whereas on the lower levels we had climbed under clear skies, now the heavens were frequently clouded over black from horizon to horizon, bringing fierce squalls of snow or hail, and a biting wind was in our teeth all day, though calming down usually at nightfall. Philipson was working towards the _obo_ very much as if it were a point in the ocean and he a mariner steering a course to it; he used his maps as a chart and checked our position by observations whenever the sky cleared. The lie of the land necessitated constant changes of direction, and sometimes we had even to deviate from Philipson's former route, which, it will be remembered, he had followed on foot; but never would our leader consent to leave the course laid down on his maps unless it was physically impossible to get the ponies along it. As it was, our journey took us up and down steeps which rise in my mind to this hour like a ghastly dream--one of those nightmares when you imagine yourself to be clinging fly-like to a vertical wall at dizzy heights. But for the energy and skill and implacable resolve of Saunders Philipson I am perfectly certain we should never have got through at all, and even he couldn't prevent the ponies from succumbing one by one to the tremendous work on scant fodder. Also, two of the _tagliks_ lost their lives in one day, slipping under their load and falling down a deep ravine. Worst of all, the _obo_ hadn't appeared, although by Philipson's calculations we should have found it by now. Philipson kept up a dogged confidence, but I could see that even he was getting uneasy. He decided, before casting around, to push straight ahead for one more day's march. This we did, and it was our worst day yet. Two ponies dropped dead, and two of the remaining bearers disappeared--where, we never discovered, though it is likely they lay down to the drowsy rest from which there is no awakening, and were quietly left by their own fellows. At last Philipson, who was on foot ahead, halted with a great cry. 'This is the pass,' he shouted. 'The _obo_ is at the top end of it.' But when we came to the place it was five or six feet deep in drifts, and nobody short of a diviner could have said whether the _obo_ was there or not. It was too late to investigate now: dark was coming on. We retreated down the rugged slope and pitched camp.