Three different methods have successively been used in the determination of longitudes of distant places. In each case the problem required was to ascertain the time at the standard place, say Greenwich, at the same time that it was being determined in the ordinary way at the given station. One method of ascertaining Greenwich time when at a distance from it was, as stated in Chapter I., to use the moon, as it were, as the hand of a vast clock, of which the sky was the face and the stars the dial figures. This is the method of 'lunar distances,' the distances of the moon from a certain number of bright stars being given in the _Nautical Almanac_ for every three hours of Greenwich time. As chronometers were brought to a greater point of perfection, it was found easier and better in many cases to use 'chronometer runs,' that is, to carry backwards and forwards between the two stations a number of good chronometers, and by constant comparison and re-comparison to get over the errors which might attach to any one of them. [Illustration: THE TRANSIT PAVILION. (_From a photograph by Mr. Lacey._)] But of late years another method has proved available. Distant nations are now woven together across thousands of miles of ocean by the submarine telegraph. The American reads in his morning paper a summary of the debates of the previous night in the House of Commons at Westminster. The Londoner watches with interest the scores of the English cricket team in Australia. It is now therefore possible for an astronomer in England to record, should he so desire, the time of the transit of a star across the wires of his instrument, not only on his own chronograph, but upon that of another observatory, it may be 2000 miles away. Or, much more conveniently, each observer may independently determine the error of his own clock, and then bring his clock into the current, so that it may send a signal to the chronograph of the other station.