A remarkable example occurs in the record of an eclipse of the sun of A.D. 664. At the present day astronomers can calculate to a minute the time of an eclipse occurring in that or any other year. But it was otherwise twelve centuries ago. Then the rules of calculation were not quite correct, so that a person calculating backwards was pretty sure to be in error as to the exact time. The great English historian and scholar, the Venerable Bede, who wrote fifty or sixty years after the above-mentioned eclipse, was aware of the year (664), but had to calculate the day and the hour. The rule then in vogue led him astray, and accordingly his record of the date--the 3rd May--is two days wrong. In the Annals of Ulster the correct date--1st May, 664--is given, and even the very hour. This shows quite clearly that the event had been recorded by some Irish chronicler, who actually saw it and noted it down on the spot. We find numbers of records of this kind in our Annals, which, according to the accurate tests we are now able to apply, are all found to be correct. Another remarkable instance of a similar kind deserves to be mentioned here. We have an old Irish book called “The War of the Irish with the Danes,” written early in the eleventh century, soon after the battle of Clontarf, in which that great battle is very fully described. In the course of his narrative the writer makes these very specific statements:--that the battle was fought on Good Friday, the 23rd April, 1014; that it commenced at sunrise _when the tide was full in_, and that it lasted the whole day till the tide was again at flood about the same hour in the evening, when the foreigners were routed. Moreover, the old historian puts in the time of high water, morning and afternoon, merely to explain why there was such terrible slaughter of the Danes in the evening; for on account of the full tide they were not able to reach their ships, which lay some distance out in the bay, whereas if it had been low water they might have waded out to them. Beyond that he was not in the least concerned about the time of high tide. The tide comes in at any particular point of the coast about every 12 hours 25 minutes, and accordingly the hour changes from day to day, so that there might be a high tide at any hour of the twenty-four: but astronomers can now calculate the exact time of high tide for any day of the month at a particular place in any year, no matter how far back. Now, the question is, was the tide really at its height on the Clontarf shore at sunrise on that fatal morning?