It is often asked how it is possible for an investigator accurately to determine the date of any picture from the far-distant past which he disinters from the records. The fact is that it is sometimes rather tedious work to find an exact date, but the thing can usually be done if it is worth while to spend the time and trouble over it. If we are dealing with Greek or Roman times the simplest method is usually to look into the mind of the most intelligent person present in the picture, and see what date he supposes it to be; or the investigator might watch him writing a letter or other document and observe what date, if any, was included in what was written. When once the Roman or Greek date is thus obtained, to reduce it to our own system of chronology is merely a matter of calculation. Another way which is frequently adopted is to turn from the scene under examination to a contemporary picture in some great and well-known city such as Rome, and note what monarch is reigning there, or who are the consuls for the year; and when such data are discovered a glance at any good history will give the rest. Sometimes a date can be obtained by examining some public proclamation or some legal document; in fact in the times of which we are speaking the difficulty is easily surmounted. The matter is by no means so simple, however, when we come to deal with periods much earlier than this--with a scene from early Egypt, Chaldaea, or China, or to go further back still, from Atlantis itself or any of its numerous colonies. A date can still be obtained easily enough from the mind of any educated man, but there is no longer any means of relating it to our own system of dates, since the man will be reckoning by eras of which we know nothing, or by the reigns of kings whose history is lost in the night of time. Our methods, nevertheless, are not yet exhausted. It must be remembered that it is possible for the investigator to pass the records before him at any speed that he may desire--at the rate of a year in a second if he will, or even very much faster still. Now there are one or two events in ancient history whose dates have already been accurately fixed--as, for example, the sinking of Poseidonis in the year 9564 B.C. It is therefore obvious that if from the general appearance of the surroundings it seems probable that a picture seen is within measurable distance of one of these events, it can be related to that event by the simple process of running through the record rapidly, and counting the years between the two as they pass.