On the opposite side of the Empire, towards the north and the north-east, in Azerbijan, on the Iranian plateau, in the Afghan plains, in the high flat region east of the Bolor, and again in the low plain about the Aral lake and the Caspian, a severe climate prevailed during the winter, while the summer combined intense heat during the day with extraordinary cold--the result of radiation--at night. Still more bitter weather was experienced in the mountain regions of these parts--in the Bolor, the Thian Chan, the Himalaya, and the Paropamisus or Hindu Kush--where the winters lasted more than half the year, deep snow covering the ground almost the whole of the time, and locomotion being rendered almost impossible; while the summers were only moderately hot. On the other hand, there was in this quarter, at the very extreme east of the Empire, one of the most sultry and disagreeable of all climates--namely, that of the Indus valley, which is either intolerably hot and dry, with fierce tornadoes of dust that are unspeakably oppressive, or close and moist, swept by heavy storms, which, while they somewhat lower the temperature, increase the unhealthiness of the region. The worst portion of the valley is its southern extremity, where the climate is only tolerable during three months of the year. From March to November the heat is excessive; dust-storms prevail; there are dangerous dews at night; and with the inundation, which commences in April, a sickly time sets in, which causes all the wealthier classes to withdraw from the country till the stagnant water, which the swell always leaves behind it, has dried up. Upon the whole, the climate of the Empire belonged to the warmer class of the climates which are called temperate. In a few parts only, indeed, as in the Indus valley, along the coast from the mouth of the Indus to that of the Tigris, in Lower Babylonia and the adjoining portion of Susiana, in Southern Palestine, and in Egypt, was frost absolutely unknown; while in many places, especially in the high mountainous regions, the winters were bitterly severe; and in all the more elevated portions of the Empire, as in Phrygia and Cappadocia, in Azerbijan, on the great Iranian plateau, and again in the district about Kashgar and Yarkand, there was a prolonged period of sharp and bracing weather. But the summer warmth of almost the whole Empire was great, the thermometer probably ranging in most places from 90° to 120° during the months of June, July, August, and September. The springs and autumns were, except in the high mountain tracts, mild and enjoyable; the Empire had few very unhealthy districts; while the range of the thermometer was in most of the provinces considerable, and the variations in the course of a single day and night were unusually great, there was in the climate, speaking generally, nothing destructive of human vigor--nothing even inimical to longevity.