masked the dam the man had been looking, and Whistler knew that the spot in which he was interested must be directly beside the overflow of the dam—where the water splashed down into the rocky river bed.

Whistler did not lose interest in the attempt to inspire some of the factory workers to enlist in the Navy, and he worked just as hard as his mates all through the noon hour. But the puzzle connected with the man named Blake continued to peck at his mind like an insistent chick trying to get out of its shell.

Hans Hertig's desire to get some of his old friends to enlist bore some fruit. Three men promised to go down to the enlistment bureau on Saturday afternoon, when they had a half holiday.

The Seacove party then wanted to go to a dining-room for dinner; but Whistler excused himself. He was hungry enough; but he "had other fish to fry," he whispered to Torrance.

"Come around by the Upper Road—same way we got here," directed Whistler. "I'll meet you at the bridge. Wait if I'm not there."

"What is the matter with you, Whistler?" demanded Al.

But although Morgan went away without making answer, he knew that his chum would do as he was asked, and bluff off the others when they asked questions, too.

Philip Morgan hurried past the factories and the few houses which lay in this direction. The land near the dam which had been built across the valley was so sterile that few people lived in this neighborhood.

Up on the ridges, on either side, were farms; but this was a wild piece of scrub at the foot of the dam. One could jump a rabbit in it, or get up a flock of quail at almost any time during the hunting season.

Like most boys of Seacove, as well as Elmvale, Whistler was familiar with this stretch of untamed ground and plunged into it with full knowledge of its tangled brier patches and rough quarries. He started diagonally for the dam, and in a brief time came to the edge of the shallow channel, which now carried the overflow of the huge reservoir behind the dam down to the cove.

As he followed this stream, he could not help thinking of the possibility of a break occurring in the high wall of masonry which loomed ahead of him. If there should be any undiscovered weakness in the wall! Or if an enemy should sink a charge of dynamite, or some other high explosive, at the base of the dam and blow a hole through it!

He did not see any one moving about the dam either above or below. He knew that on the ridge, level with the top of the barrier, lived a man they called the dam superintendent. He sometimes walked across the embankment, from end to end; a privilege forbidden to others.

But Whistler was quite sure that this dam superintendent seldom went to the foot of the wall, or examined the face of it for any break in the stonework. Of course, the dam had stood secure for so many years that it seemed improbable that it would fail in any part now.

But Whistler Morgan was not considering any leakage of the water through the masonry which might endanger the foundation of the dam. Such seepage must have shown itself long ago if the barrier had not been properly constructed.

It was of a sudden, unexpected, and treacherous blow-out that the young sailor was thinking. That man in the bushes, who had seemed so desirous of hiding from the passers-by and whose interest in the face of the dam had been so marked, puzzled Phil and excited his suspicions.

Blake. And Blake was an English name! He looked about as much like an Englishman as he, Whistler, looked like Dinkelspiel!

"I have seen plenty of Britishers," thought the young fellow, "and not one of them ever looked like this chemist, or whatever he is. And he's a stranger—worked here only a month.

"He was not tapping rocks or getting botanical specimens over here when we fellows came along the Upper Road. His interest was in this dam—if it was at long distance. I wonder if we ought to report him to the marshal's office.

"And get him, if he's innocent of any wrongdoing, into hot water," Whistler added, wagging his head. "Say! that won't do. We fellows came near getting poor Seven Knott into trouble, thinking him a German spy," he added, referring to an incident mentioned in "Navy Boys After the Submarines."

Thus meditating he drew nearer to the place where the flashboard was down and the water poured into the rocky river bed. There were stepping stones here, so it was easy for an agile person to get across the stream.

A blue haze of spray rose from the foaming water on the rocks, and there sounded a pleasant murmur from the falling water. Birds darted in and out of this spray, fluttering their pinions in the bath thus provided.

On this side of the waterfall Whistler could discover nothing on the face of the dam nor along its foot that seemed in the least suspicious. The masonry was perfect.

He crossed the river bed, leaping from stone to stone, and stepped up so close to the falling water that the spray splashed him. It was somewhere about here, he thought, that the man, Blake, had focused his field-glass from the roadside.

There was absolutely nothing out of the way here that he could see. The brush was kept cleared out at the foot of the dam for a dozen feet or so; there seemed to be no cover here. Not a stone had been overturned along this cleared path.

The water splashed and bubbled at the foot of the fall. Did it seem to splash more vigorously just here at the edge of the pool, hidden by the spray in part, and partly by the overhang of a great rock on which Whistler stood?

The observant youth stooped, then knelt beside the stream. The rock was wet and his garments were fast becoming saturated. But he paid no attention to this.

There was something down there in the pool, at its edge, struggling beneath the surface. Not a fish, of course!

Suddenly he thrust in his hand, wetting his sleeve to the elbow. Quickly he made sure that his suspicion was correct. There was some kind of water wheel whirling down there.

He moved a flat stone which seemed to have lain for ages in its present position. Yet under that stone was the end of the wheel's axle with cogwheels rigged to pass on the power engendered by the wheel to some mechanical contrivance not yet placed.

Whistler returned the flat rock back to its former position, and moved slowly back from the place on hands and knees. Then he stood up and looked all around to see if he had been observed. Particularly did he look through the break in the trees toward the spot where Blake, the stranger, had stood when Whistler and his friends had first spied him.

There was nobody in sight as far as the young fellow could see. He moved back into the shelter of a clump of brush. He heard an automobile chugging up from the village and believed Al and the others were approaching the bridge where he had asked his chum to wait for him.

But he lingered a bit. He was deeply moved by his discovery. This was no boy's plaything. The mechanism was the effort of a mature mind, perhaps the result of inventive genius of high quality.

Some inventor might be secretly experimenting with water power here; and if Whistler told of his discovery he might be doing the unknown a grave wrong.

Yet Blake's peculiar actions and the fact that the foot of the dam had been chosen for the experiment troubled the young fellow vastly.

There was nothing along the wall, as far as he could see, or upon its face, that excited Whistler's further suspicion. Just that little water wheel under the rock whirling and splashing by the power of the falling stream. It was perfectly innocent in itself; yet Philip Morgan