As in the Polar regions, also, the weather decides between success and failure, between return and no return. Because of the cold, it is unwise to start before sunrise.[28] The risk is less in descending easy ground at night—perhaps because movement is then quicker.
A concrete example puts the case shortly. Trisul is only some 23,400 feet high, but it appears to be the highest peak of which the complete ascent is universally admitted. After two nights, at about 20,000 feet, in bad weather, the party retreated to 14,000 feet. Three days later, after one bivouac at about 18,000 feet, the summit was reached at 4 p.m. (10 hours), and the night was spent on the return at about 16,500 feet.
Season.
Generally speaking, the regular rainy season (‘monsoon’) commences in July and ends in September; but all the world over more rain falls, and falls more frequently, on mountains than on the country immediately surrounding them. Hence, though probably June is the best month for the high peaks, we cannot even then count on continuous fine weather.
It is always easy to avoid the monsoon by pushing north into the second range; but here again it must not be expected that the highest peaks will completely conform to the rainless character of the rest of this region.
When the rains are over, in September and October spells of gloriously fine and clear weather are the rule; but the nights are then bitterly cold above the tree-line.
The Chief Districts
Though the Himalaya, in the widest sense of the term, extend beyond the Brahmapootra on the east and beyond the Indus on the west, we may impose these limits upon them for present purposes. Furthermore, only sections of these ranges are at present politically accessible to the mountaineer.
Practically the whole of the Himalayan region is covered by the Great Trigonometrical Survey of India on a scale of one inch to four miles. The sheets are obtainable in London.
It would be easy to criticize this map in detail. For reasons of finance and policy, the surveyors were ordered to cover a very large area each season and not to attempt detailed surveys of uninhabited areas. It would be, therefore, manifestly unfair to set up claims which were never made by the authors and then to demolish them.[29]