The Oriental rain-stones noted by pseudo-Aristotle and by many other Arabic writers of medieval times, can be paralleled by similar rain-making or rain-inducing stones in many other parts of the world and among many primitive peoples even in modern times. The rain-makers of the African tribe of Wahumas, dwelling in the region bordering on the great Albert Nyanza Lake in Central Africa, use a black stone in the course of their magic rites. This is put into a vessel and water poured over it; the pulverized roots of certain herbs and some blood drawn from the veins of a black goat are then mixed with the water, and the resulting liquid mixture is thrown up into the air by the rain-maker.[10] The sorcerers among the Dieri in Central Australia place such trust in the efficacy of these conjurations as to believe that all rainfalls are produced thereby, generally through the intermediate action of ancestral spirits. If rain falls in a locality where no proceedings of the kind have taken place, then it is supposed that they have been initiated in some contiguous territory, a merely spontaneous and natural rainfall being out of the question. The clouds indeed generate the rain, but it will not be brought to the earth except by magic art. In the complicated magic ceremonies of these Dieri rain-makers, two large stones are employed; after a ceremonial, in the course of which the blood drawn from the two chief sorcerers is smeared over the bodies of the others, the stones are borne away by these two sorcerers for a distance of about twenty miles, and there put far up on the highest tree that can be found, the object evidently being to bring them as near to the clouds as possible.[11] Rock-crystal as a rain-compeller finds honor among the wizards of the Ta-ta-thi tribe in New South Wales, Australia. To bring down rain from the sky one of them will break off a fragment from a crystal and cast it heavenward, enwrapping the rest of the crystal in feathers. After immersing these with their enclosure in water, and leaving them to soak for a while, the whole is removed and buried in the earth, or hidden away in some safe place.[12] The widely spread fancy that rock-crystal is simply congealed water may have something to do with the choosing of this stone as a rain-maker. Sumatrans of Kota Gadanz use a stone whose form roughly resembles that of a cat in their invocations of rain, a live black cat being supposed in some parts of this island to have certain rain-producing virtues.[13] Perhaps the electric fur of the animal may have suggested a connection with thunder-storms. Stones of this type, indeed a great many of those to which magic properties are attributed, are in many cases smeared with the blood of fowls, or have incense offered to them, this treatment of such stones being observed by the peasants in Scandinavia and other parts of Europe as well as in the Far East.