The accompanying diagram is an illustration of rock disintegration in the Sahara. There is no tangible counteraction to these advances of decay, and it would seem that they are destined irrevocably to continue. But on this score the question of rainfall is intensely interesting, for should the elements ever be kind, and really good and consistent rains fall for two or three years in succession, the whole land would undoubtedly revive its vegetation with astonishing speed. Perhaps such revivals have occurred in the past, and may occur again. But I fear that, at best, they can be but short-lived. Indeed, conditions at the present are the opposite, and the prospect is that they will so continue. One hears from the nomads of regions having no rain for three years, four years, and even seven years; while have I myself seen _had_ dried out and dead, though natives declare that it never dies except when there are more than four rainless years. The Sahara is not yet devoid of vegetation, but its poverty is advancing. To-day we find the old caravan roads across Africa unfrequented—the Cyrenaican-Kufra-Wadai road, the Tripoli-Bilma-Chad road, the Tunis-Tripoli-Ghat-Aïr-Kano road: all of great antiquity, and from time immemorial the trade routes across North Africa. These roads are still to be seen, ten to fifteen parallel paths, camel-width apart, with undiminished clearness, where they pass over stony ground, powdered down to clean-cut furrows by passage of countless feet. They are steeped in the romance and mystery of the Sahara. Over them have passed hard-won pilgrimages to Mecca, cavalcades of slaves fettered and limb-weary and fearful, and rich caravans of merchandise that reached their goal or were looted—a gamble that made or lost a fortune for the masters who sent them forth. To-day they are unused, and the commerce of the Sahara is dead. And this is comprehensible when the poverty of the land is reviewed and the belief held that growing dearth of vegetation has made it well-nigh impossible for large caravans to live to-day on those roads. The same melancholy decline is to be found among the people of the Sahara. Its population is scattered and thin, and some regions are uninhabited altogether. We can only approximately estimate the numbers in the interior, which I believe, from data collected, to be about 40,000. Say 200 to 600 in oases here and there at wide intervals; 5,000 in the Aïr region; 5,000 in Ahaggar, and 10,000 Tebu in Tibesti; roughly, about one human soul to every sixty square miles.