Juba says, that in the country of the Troglodytæ there is a lake, called the "Lake of Insanity,"[1] from its highly noxious properties: thrice a day it becomes salt and bitter, and then again fresh, the same taking place as many times during the night. It is full, he says, of white serpents, twenty cubits long.[2] He mentions, also, a certain spring in Arabia, which rises from the ground with such remarkable force, as to throw back any object pressed down upon it, however weighty.