If a beacon throws a fixed light, unless it is of extreme power, it is liable to be confused with a ship’s mast-light, a fact which was found to be one of the greatest objections to the fixed white light of the acetylene aid to navigation. On the other hand, a flashing warning must be of such a character that it cannot be mistaken for the twinkling of a brilliant star, or of a light which has nothing to do with navigation. This is where the “Aga” flasher emphasizes its value. It throws a short, powerful gleam at brief intervals. The mariner cannot possibly confuse or misconstrue it; the regularity of the flash arrests his immediate attention, and its purport may be divined instantly. The apparatus is simple and highly effective, while it has the advantage that the periods of light and darkness can be altered in relation to one another, or grouped, as desired. From the maintenance point of view, however, the invention is of far greater significance. As the gas is consumed only during the light periods, which are very brief in comparison with the eclipse, the economy effected is very appreciable. When the apparatus was first brought within the range of practical application, many authorities, which had become wedded to the oil-gas lighting system, wherein the light flashes are of long duration in comparison with the dark periods, maintained that the Dalén flash was too short to be of any value. They disregarded the fact that the power of the acetylene-gas flash is about seven times as intense as that of the oil-gas light. For instance, when the United States acquired the first Aga light in the autumn of 1908, the authorities demanded either a characteristic signal comprising ten seconds of light followed by five seconds of darkness, or flashes and eclipses of equal duration--five seconds. [Illustration: THE “SVINBĀDAN,” UNATTENDED LIGHTSHIP IN SWEDISH WATERS. It works upon the Dalén system with flasher, giving a flash of 0·3 second duration, followed by darkness for 2·7 seconds.] There was a prejudice against short, powerful, and oft-repeating flashes, mainly because their advantages were misunderstood. Practical experience, however, demonstrated the fact that the period of light might be reduced very considerably, and, as a result of prolonged investigations, the Swedish Board of Pilotage adopted a characteristic comprising 0·3 second light followed by darkness for 2·7 seconds. This has become known since as the “one-tenth flash,” owing to the luminous interval occupying one-tenth of the combined period of light and darkness. It will be seen that, as a result of this arrangement, twenty flashes are thrown per minute.