In due course the cases with their precious contents reached the site of erection, but unfortunately the season was so far advanced that the engineer concluded he could not complete the erection of the lantern before the monsoon broke. As the contents of the cases were preserved by the tin armour from climatic attacks, he stored the cases securely, and with his workmen left the place until favourable weather returned. Some weeks later the chief and his toilers reappeared upon the scene. All preparations for setting the optical apparatus were completed. Imagine the dismay of the engineer when, on opening the case containing the most important parts of the lantern, he found that it had been raided by white ants. They had driven their tracks spirally through the tow, which evidently they had enjoyed, and although this was of little consequence, the formic acid had played sad havoc with the bright surfaces of the spindles. In lighthouse engineering the surfaces of these parts must be as bright and as clean as a mirror to insure smooth, steady working. But now these spindles were as pitted and marked as a victim to smallpox. It was a maddening contretemps, since the only way to restore the vital bright surfaces was to turn them in the lathe. Such a tool was not available within a hundred or more miles. Erection had to be delayed, however, until this treatment was effected. Seeing that the tin case was soldered up with such infinite care, the question arises. How did the ants get into it? To the engineer it seemed an inscrutable puzzle, but he subjected the case to a minute examination. Finally he solved the problem. At one corner he found that a nail, while being driven during the process of nailing up the heavy outer wooden case at the English factory, had turned slightly, so that its point had punctured the inner metal case. The ants, too, had discovered this minute breach, and through it had swarmed to the attack upon the interior. CHAPTER XXI UNATTENDED LIGHTHOUSES During the past fifty years engineering science as applied to lighthouses has made remarkable advances. This has been due largely to the indefatigable perseverance and ceaseless labour of the chemist in regard to illumination. This wonder-worker has given us acetylene, has evolved means whereby oil-gas may be compressed to a pressure of several atmospheres with safety, and has discovered other gases obtainable by inexpensive and simple means. The engineer has not hesitated to profit from these developments, and has devised highly ingenious apparatuses whereby these illuminating mediums may be stored and used, so as to dispense with the human element almost entirely; in fact, in these instances the latter factor has been reduced to such a degree that it is only called upon to perform certain perfunctory operations, such as the recharging of the storage vessels at long intervals--three, six, or twelve months, according to circumstances.