And this particular night's scouting proved as tame and uneventful as the rest. Under normal conditions, a night flight above the Firth of Forth as far west as Linlithgow would have afforded a most picturesque spectacle with the lighted towns and cities beneath. But now Edinburgh, Linlithgow, and Dundee, and even the small towns and villages, were practically in darkness, since nearly all the public lights, besides those of the great emporiums and factories, were either unlit or else shielded from observation above. And out at sea only merchant vessels showed lights, those carried by warships, large and small, being masked. "Even the passenger flights at Hendon were more exciting than this!" growled the Lieutenant to himself as, just before dawn, he steered a homeward course in the direction of the Forth. He little thought as he uttered his complaint that within twenty-four hours he would have had enough excitement to last him a lifetime. The machine had reached the Forth and was crossing it just above the bridge, when Mike, who sat immediately behind the Lieutenant, uttered an exclamation: "Are me eyes desaving me, or have the hivins turned topsy-turvy?" "What's the matter?" asked Lawless, for the patent wind-screen with which the machine was fitted made conversation possible even when travelling at a high speed. "Thim stars below us, sorr. Sure now, is it upside down we're flying?" Lawless looked below, and saw what at first seemed to justify Mike's anxiety as to the position of the heavens. Immediately beneath the machine was a cluster of luminous specks for all the world like distant stars, shining up instead of down upon them. They were certainly not lamps of any sort, and the dull glow they gave out seemed as if it might be the reflection of some distant lights. Yet there was no moon, nor, so far as Lawless could discover, anything which could account for this extraordinary effect of reflected light. He circled over the bridge two or three times, hoping to discover the cause of this mystery, but without success. While he was doing this a train rumbled across the bridge, and during its passage Lawless noted that the luminous specks disappeared. They were again observable as soon as the train had passed, however, and the Lieutenant concluded from this that they were situated on the railway track itself. "Deuced queer business!" he muttered. But there was no time to make further investigations that night, so he continued his flight to Montrose, still pondering over the mystery. "By the way, Mike," he said, when they had alighted opposite the hangar, "don't say anything about those lights we saw on the bridge. I'm going to investigate the matter myself." Mike readily promised, and Lawless was strolling away when a thought suddenly struck him. "By Jove!" he ejaculated aloud. "I believe I've got it!"