Millenial Celebration of Karaji's Hydrology

A brief account of Mohammed Karaji, a Persian scholar of the tenth century, and his contributions to science, especially ground-water hydrology, is presented. Karaji wrote the first algebra text presented with symbolism. In engineering, he invented instruments that proved useful in the surveying and in the tunneling of underground chanels for conveying water. Most importantly, he expounded the basic principles of hydrology, understanding the proportionality law between the force of gravity and the mass of a body. Karaji noted that ground-waters, like surface waters, can be stagnant, and that still waters can be located under vast deserts and lowlands. A recently discovered text by Karaji on hidden water is the oldest known text on ground-water hydrology.