An Arab once said to Rabbah bar Channah, "Come and I will show thee the place where Korah and his accomplices were swallowed up." "There," says the Rabbi, "I observed smoke coming out from two cracks in the ground. Into one of these he inserted some wool tied on to the end of his spear, and when he drew it out again it was scorched. Then he bade me listen. I did so, and as I listened heard them groan out, 'Moses and his law are true, but we are liars.' The Arab then told me that they come round to this place once in every thirty days, being stirred about in the hell-surge like meat in the boiling caldron." _Bava Bathra_, fol. 74, col. 1. Rabbi Yochanan, in expounding Isa. liv. 12, said, "The Holy One--blessed be He!--will bring precious stones and pearls, each measuring thirty cubits by thirty, and polishing them down to twenty cubits by ten, will place them in the gates of Jerusalem." A certain disciple contemptuously observed, "No one has ever yet seen a precious stone as large as a small bird's egg, and is it likely that such immense ones as these have any existence?" He happened one day after this to go forth on a voyage, and there in the sea he saw the angels quarrying precious stones and pearls like those his Rabbi had told him of, and upon inquiry he learned that they were intended for the gates of Jerusalem. On his return he went straight to Rabbi Yochanan and told him what he had seen and heard. "Raca!" said the latter, "hadst thou not seen them thou wouldst have kept on deriding the words of the wise!" Then fixing his gaze intently upon him, he with the glance of his eye reduced to a heap of bones the carcass of his body. Ibid., fol. 75, col. 1. He who lends unconditionally a sum of money to his neighbor is not entitled to demand it back within thirty days thereafter. _Maccoth_, fol. 3, col. 2. If a man has lost a relative, he is forbidden to engage in business until thirty days after the death. In the case of the decease of a father or a mother, he is not to resume work until his friends rebuke him and urge him to return. _Semachoth_, chap. 9. It is unlawful for one to enter a banqueting-house for thirty days after the death of a relative; but he must refrain from so doing for twelve months after the demise of either father or mother, unless on the behest of some higher requirement of piety. Ibid. But I know not whether there are thirty righteous men here and fifteen in the land of Israel, or _vice versâ_. _Chullin_, fol. 92, col. 1. Thirty days in a year are equivalent to a whole year. _Niddah_, fol. 44, col. 2. "Moses, thou didst say unto me, 'What is Thy name?' And now thou dost say, 'Neither hast Thou delivered Thy people at all.' Now shalt thou see what I will do to Pharaoh (Exod. v. 23, vi. 1), but not what I am about to do to the thirty-one kings." _Sanhedrin_, fol. III, col. 1.