Calling out to Taggert to steady the _Sphere’s_ course, Robert carefully aimed the tube into the thickest of the invaders where Taggert played the searchlight’s shaft back and forth. Robert pulled the lever releasing the lightning bolt! A blinding flash, and a rending crash followed! The _Sphere_ vibrated like a violin string. Only the goggles which they wore made it possible for Robert and Taggert to look upon the jagged pillar of incandescent flame which spattered upon the plain below with terrific force. So swift and brilliant was its course, that almost ere it had registered upon the retina of their eyes, it was gone, leaving them nearly powerless to see. When they were again able to see and hear with fair distinctness, they became aware of a great hubbub below. The firing of the artillery had ceased and the attack of the invaders had turned into a rout. Hakon’s men were driving them back like sheep! “God!” ejaculated Taggert, for once jarred out of his habitual sangfroid. Robert was silent. A vast pit was visible where the bolt had struck, and the bodies of hundreds of men were strewn round it. The demoralization of that division for the present was complete. The destructive force of the bolt was appalling, but the spectacle it presented had been even more so. The invaders were terrified beyond control by panic fear of this leaping bolt of fire from above. Robert had no desire to take lives unnecessarily: If the first bolt was sufficient to cause the invaders to retreat or to cease fighting, he determined not to release a second one. He studied closely the movements of the armies. As if afraid to antagonize the _Sphere_ further, the invaders had ceased to play the beams of their searchlights upon it. In the east the first faint flush of dawn was visible. Already the tall spires of the metropolis were touched with coral. Robert became aware that the _Sphere_ had settled too close to the ground for safety in case of further firing from the hostile artillery. “Better raise her another thousand, Taggert,” he called, turning to the latter, who was operating the machinery. “Just what I was trying to do, old man, but she doesn’t respond.” A swift examination proved Robert’s fears--that their reserve of power had been virtually exhausted by the tube! The speed of the gyrostats was perceptibly slackening. The _Sphere_ was sinking! Feverishly they turned to the engine which drove the dynamo. With this running, enough current soon would be generated to lift the _Sphere_ out of danger. It was then that the extent of their calamity was discovered. The engine stubbornly refused to start, for one of those mysterious reasons to which engines are addicted. It persistently defied their combined efforts to diagnose the trouble.