During the period of the Jewish restoration, up to the destruction of Jerusalem by Titus, the Sanhedrim used to sit in the "Hall of Polished Stones" to receive the testimony of credible witnesses that they had seen the new moon. If the new moon had appeared at the commencement of the 30th day--corresponding to our evening of the 29th--the Sanhedrim declared the previous month "imperfect," or consisting only of 29 days. If credible witnesses had not appeared to testify to the appearance of the new moon on the evening of the 29th, the next evening, _i. e._ that of the 30th--according to our mode of reckoning--was taken as the commencement of the new month, and the previous month was then declared to be "full," or of 30 days. Early in the Christian era, it was enacted that no testimony should be received from unknown persons, because, says the Talmud, the Baithusites wished to impose on the Mishnic Rabbis, and hired two men to do so for four hundred pieces of silver. It is clear, therefore, that about the time of the Christian era the beginnings of the months were determined astronomically from the actual observation of the new moons, and we may safely conclude that it was the same also from the earliest times. It was the actual new moon, not any theoretical or fictitious new moon, that regulated the great festivals, and, as we have seen, there was often some considerable uncertainty possible in the fixing of the dates. The witnesses might give conflicting testimony, and the authoritative date might be proved to be in fault. We have an instance of such conflicting authority in the different dating, on one occasion, of the Day of Atonement by the Rabbi Yehoshua, and Rabbon Gamaliel, the president of the Sanhedrim, grandson of the Gamaliel at whose feet Paul sat. According to a statement in the Mishna, dating from the second century of our era, the appearance of the new moon at Jerusalem was signalled to Babylonia during the century preceding the destruction of the Holy City by Titus, and perhaps from earlier times. The dispersion of the Jews had therefore presented them with an additional difficulty in fixing the beginning of their months. The problem is much more intricate to-day, seeing that the Jews are dispersed over the whole world, and the new moon, first visible on one evening at Jerusalem, might be seen the evening before, according to the reckoning of places west of Jerusalem, or might be invisible until the following evening, according to the reckoning of places east of it. We have the same problem to solve in finding the date of Easter Sunday. The Prayer Book rule for finding it runs thus:-- "Easter day is always the first Sunday after the full moon which happens upon, or next after, the 21st day of March; and if the full moon happens on a Sunday, Easter day is the Sunday after."