Grislow gave it up at that and went back to the original contention.

"We're dodging the main issue," he said. "What is the active principle of your 'sevens' – or haven't you figured it out?"

"Change," was the prompt rejoinder; "always something different – radically different."

"And what started you off into the memory woods, particularly, to-night?"

"A small recurrence of the coincidences. It began with that hopelessly unreliable little clock that Anson persists in carrying around with him wherever he goes. While you were up on the hill cutting your spruce tips Anson pulled out and said he was going to unpack his camp kit. He went over to his tent and lighted up, and a few minutes afterward I heard the clock strike – seven. I looked at my watch and saw that it lacked a few minutes of eight, and the inference was that Anson had set the clock wrong, as he commonly does. Just as I was comfortably forgetting the significant reminder the clock went off again, striking slowly, as if the mechanism were nearly run down."

"Another seven?" queried Grislow, growing interested in spite of a keen desire to lapse into ridicule again.

"No; it struck four. I didn't imagine it, Murray; I counted: one – two – three – four."

"Well?" was the bantering comment. "You couldn't conjure an omen out of that, could you? You say there was a light in the tent – I suppose Anson was there tinkering with his little tin god of a timepiece. It's a habit of his."

"That was the natural inference; but I was curious enough to go and look. When I lifted the flap the tent was empty. The clock was ticking away on Anson's soap-box dressing-case, with a lighted candle beside it, and for a crazy half second I had a shock, Murray – the minute-hand was pointing to four and the hour-hand to seven!"

"Still I don't see the miraculous significance," said the hydrographer.

"Don't you? It was only another of the coincidences, of course. While I stood staring at the clock Anson came in with Griffith's tool kit. 'I've got to tinker her again,' he said. 'She's got so she keeps Pacific time with one hand and Eastern with the other.' Then I understood that he had been tinkering it and had merely gone over to Griffith's tent for the tools."

"Well," said Grislow again, "what of it? The clock struck seven, you say; but it also struck four."

Brouillard's smile tilted his curling mustaches to the sardonic angle.

"The combination was what called the turn, Grizzy. To-day happens to be my twenty-eighth birthday – the end of the fourth cycle of seven."

"By George!" ejaculated the hydrographer in mock perturbation, sitting up so suddenly that he dropped his pipe into the ashes of the fire. "In that case, according to what seems to be the well-established custom, something is due to fall in right now!"

"I have been looking for it all day," returned Brouillard calmly, "which is considerably more ridiculous than anything else I have owned to, you will say. Let it go at that. We'll talk about something real if you'd rather – that auxiliary reservoir supply from the Apache Basin, for example. Were the field-notes in when you left Washington?" And from the abrupt break, the technicalities came to their own again; were still holding the centre of the stage after the groups around the mess fires had melted away into the bunk shelters and tents, and the fires themselves had died down into chastened pools of incandescence edged each with its beach line of silvered ashes.

It was Murray Grislow who finally rang the curtain call on the prolonged shop-talk.

"Say, man! do you know that it is after ten o'clock?" he demanded, holding the face of his watch down to the glow of the dying embers. "You may sit here all night, if you like, but it's me for the blankets and a few lines of 'tired Nature's sweet restorer, balmy' – Now, what in the name of a guilty conscience is that?"

As it chanced, they were both facing toward the lower end of the valley when the quotation-breaking apparition flashed into view. In the deepest of the shadows at the mouth of the gorge, where the torrenting Niquoia straightened itself momentarily before entering upon its plunging race through the mountain barrier, a beam of white light flickered unsteadily for a fraction of a second. Then it became a luminous pencil to trace a zigzag line up the winding course of the river, across to the foot-hill spur where the camp of the Reclamation-Service vanguard was pitched, and so on around to the base of Chigringo. For certain other seconds it remained quiescent, glowing balefully like the eye of some fabled monster searching for its prey. Then it was gone.

Grislow's comment took the form of a half-startled exclamation.

"By Jove! wouldn't that give you a fit of the creepies? – this far from civilization and a dynamo?"

"It wasn't an electric," returned Brouillard thoughtfully, apparently taking Grislow's suggestion literally. "It was an acetylene."

"Supposing it was – what's the difference? Aren't we just as far from a carbide shop as we are from the dynamo? What are you calling it?"

"Your guess is as good as mine," was the half-absent reply. Brouillard was still staring fixedly at the distant gulf of blackness where the mysterious light had appeared and disappeared.

"Then I'll make it and go to bed," said the hydrographer, rising and stretching his arms over his head. "If it had come a couple of hours ago we should have called it the 'spot-light,' turned on to mark the end of your fourth act and the beginning, auspicious or otherwise, of the fifth. Maybe it is, anyway; maybe the property-man was asleep or drunk and forgot to turn it on at the spectacular instant. How will that do?"

Brouillard had got upon his feet and was buttoning his many-pocketed shooting-coat.

"It will do to put you into the Balaam saddle-beast class, Grizzy," he said, almost morosely. Then he added: "I'm going to take a little hike down yonder for investigative purposes. Want to come along?"

But the mapper of watersheds was yawning sleepily. "Not on your tintype," he refused. "I'm going to 'cork it orf in me 'ammick.' Wake me up when you come back and tell me what the fifth act is going to do to you. The more I think of it the more I'm convinced that it was the spot-light, a little overdue, after all." And he turned away chuckling.

It was only a short mile from the camp on the inward slopes of the eastern foot-hills to the mouth of the outlet gorge, across which Brouillard could already see, in mental prevision, the great gray wall of the projected Niquoia dam – his future work – curving majestically from the broken shoulder of Chigringo to the opposing steeps of Jack's Mountain. The half-grown moon, tilting now toward the sky-line of the western barrier, was leaving the canyon portal in deepest gloom. As Brouillard swung along he kept a watchful eye upon the gorge shadows, half expecting a return of the mysterious apparition. But when he finally reached the canyon portal and began to seek for the trail which roughly paralleled the left bank of the stream the mystery was still unexplained.

From its upper portal in the valley's throat to the point where the river debouches among the low sand-hills of the Buckskin Desert the canyon of the Niquoia measures little more than a mile as the bird flies, though its crookings through the barrier mountains fairly double the distance. Beginning as a broken ravine at the valley outlet, the gorge narrows in its lower third to a cliff-walled raceway for the torrent, and the trail, leaving the bank of the stream, climbs the forested slope of a boundary spur to descend abruptly to the water's edge again at the desert gateway, where the Niquoia, leaping joyously from the last of its many hamperings, becomes a placid river of the plain.

Picking his way judiciously because the trail was new to him, Brouillard came in due time to the descending path among the spruces and scrub-pines leading to the western outlook upon the desert swales and sand-hills. At the canyon portal, where the forest thinned away and left him standing at the head of the final descending plunge in the trail, he found himself looking down upon the explanation of the curious apparition.

None the less, what he saw was in itself rather inexplicable. In the first desert looping of the river a camp-fire of piñon knots was blazing cheerfully, and beside it, with a picnic hamper for a table, sat a supper party of three – two men and a woman – in enveloping dust-coats, and a third man in chauffeur leather serving the sitters. Back of the group, and with its detachable search-light missing, stood a huge touring-car to account for the picnic hamper, the dust-coats, the man in leather, and, doubtless, for the apparitional eye which had appeared and disappeared at the mouth of the upper gorge. Also it accounted, in a purely physical sense, for the presence of the picnickers, though the whim which had led them to cross the desolate Buckskin Desert for the dubious pleasure of making an all-night bivouac on its eastern edge was not so readily apparent.

Being himself a Bedouin of the desert, Brouillard's first impulse was hospitable. But when he remarked the ample proportions of the great touring-car and remembered the newness and rawness of his temporary camp he quickly decided that the young woman member of the party would probably fare better where she was.

This being the case, the young engineer saw no reason why he should intrude upon the group at the cheerful camp-fire. On the contrary, he began speedily to find good and sufficient reasons why he should not. That the real restraining motive was a sudden attack of desert shyness he would not have admitted. But the fact remained. Good red blood with its quickenings of courage and self-reliance, and a manful ability to do and dare, are the desert's gifts; but the penalty the desert exacts in return for them is evenly proportioned. Four years in the Reclamation Service had made the good-looking young chief of construction a man-queller of quality. But each year of isolation had done something toward weakening the social ties.

A loosened pebble turned the scale. When a bit of the coarse-grained sandstone of the trail rolled under Brouillard's foot and went clattering down to plunge into the stream the man in chauffeur leather reached for the search-light lantern and directed its beam upon the canyon portal. But by that time Brouillard had sought the shelter of the scrub-pines and was retracing his steps up the shoulder of the mountain.