But during this week they had had a glimpse of the Mortlake machine in flight.  One still, breathless morning, the air had been filled, soon after dawn, with a vibrant buzzing sound, which Peggy’s trained ear had recognized as the song of an aeroplane engine.

She hastened to her brother’s room and rapped upon the door.  In reply to his sleepy query, the girl rapidly told him of what she had heard.  Roy’s window faced on the road, and a glance satisfied him that the Mortlake machine was to have its first try-out.  Hastily as he dressed, however, he found that Peggy was before him on the dewy lawn, field glasses in hand.

Down the road could be seen, in front of the Mortlake plant, a small crowd of mechanics with one or two dominant figures moving among them.  With the glasses, they had no difficulty in making out Mortlake’s heavy-shouldered figure, and the slender, upright form of Lieut.  Bradbury.  All at once the group opened up a bit and they saw a silvery, glittering aeroplane, agleam with new aluminum paint, throbbing and vibrating, as if anxious to be off.  Blue smoke eddied up as the motor roared and whirred.  The air seemed to vibrate under the sound as if a battery of gatling guns had been discharged.

Fascinated, brother and sister watched the spectacle intently.  They saw Mortlake clamber heavily into the machine, followed by Lieut.  Bradbury.  A mechanic started for the front of the plane and began swinging the propeller.

“At least they haven’t cribbed our self-starting device,” exclaimed Peggy, as she saw.

The next instant the propeller became a whirring blur, and the aeroplane, after a brief preliminary run, began to climb upward.  The morning sun caught its silvered planes and turned them to gold.  It was a beautiful and inspiring sight.  Even with all that lay at stake, Peggy and Roy could not deny the machine a meed of praise.  It was fairy-like in its delicacy of construction, and speedy as a flash.

Thundering like an express train, it dashed above the Prescott home, leaving in its wake the pungent odor of burning castor-oil—­the most suitable lubricant for aeroplanes.

Then suddenly—­as if a recollection of Peggy’s mischievous flight of a few days previously had occurred to him—­Mortlake swung the delicate silvery machine about and dashed straight down at the boy and girl standing by the garden gate.  So close to their heads did he skim in his desire to show off, that he almost came too low.  For one instant it looked as if the machine would be dashed to a premature end, but it recovered buoyancy like a keeled-over racing yacht, and tore upward into the sky at an increased speed.

“Let’s get out the Golden Butterfly and follow the——­”

“Silver Cobweb!” cried Roy, the name occurring to him in a flash of inspiration as he watched the filmy outlines of the other aeroplane melt in the distance.

“Oh, Roy, what a pretty name.”