"Such as?"

"Breaking a leg by a fall, or something like that," the boy responded.

"I don't see what business any man on the Survey has to fall. That isn't what he's there for. He's there not to fall. Personally, I have never had any accidents which would need other than ordinary attention, nor have I had any with any members of my party. Then an injury would have to be pretty bad, any way, that couldn't wait until some kind of a doctor was reached, that is unless it was in the north of Alaska, or some place like that, and in such trips a little surgical case is sent along, and the chief would do as well as he could do with it."

"Then," said Roger with a short laugh, "I'm just as glad that I'm not at the bottom of the quag, for your sake as well as my own, for I should hate to be the one to spoil the Survey's record."

But while Roberts was expected in camp shortly, a couple more weeks rolled away before the party, completing its line through a very difficult piece of marsh, headed for one of the famous corduroy roads and made its way back to headquarters. There, with one of the farmer's children on his knee and the others grouped around him sat Roberts, occupied apparently in telling some interesting story or fairy tale. He put down the youngster and shouted as the party hove in sight.

The chief was delighted without question to see the newcomer, for while he had been greatly pleased with Roger, the boy could not be expected to be as valuable as an experienced man, and was not to be depended on to proceed in his work without instruction and supervision.

"I was looking for you a couple of weeks ago, Mr. Roberts," he said.

"I expected to be here earlier, Mr. Field," answered the other, "but Mr.

Herold asked me to put in a few days in that Susquehanna flow-measurement business, and that put me back."

Roger looked inquiringly at his chief, who catching his look of question, said,

"Well, son?"

"I would like to ask," said the boy hesitatingly, "what that stream flow-measurement is for?"

Roberts looked up a little surprisedly, but a few words from Fields explained the situation, and the newcomer turned to Roger quite affably.

"Certainly, my boy, it's very simple," he said. "You see, all work on rivers, whether for the purpose of irrigation, flood control, or navigation, is dependent on the amount of water that flows through that river channel every year. A week of wet weather makes a vast difference to the amount of water the river is carrying, and a dry spell cuts it off."

"But don't springs and things keep the water about even?" queried the boy.

"No, indeed," answered his informant emphatically. "Why, the Tennessee River, which I worked on once, for three months never flowed more than 20,000 cubic feet per second, yet that same year, for fifteen days in the spring, it tore down with over 360,000 feet a second. In other words, in the spring it was as big as eighteen rivers its usual size."

[Ill.u.s.tration: MEASURING STREAM FLOW.

Trolley line one mile long, over an Eastern river. Instruments pulled up, ready for return to the bank.

_Photograph by U.S.G.S._]

"Are all rivers like that?"

"Most of them. You see, suppose in the middle of summer a river is ten feet deep with a three-mile current, in the autumn is only four feet deep with a two-mile current, but in the spring floods goes rushing through its bed forty feet deep with a ten-mile current, it makes a mighty difference to the towns and villages all the way along. The destructiveness of a flood lies in the top few feet of water. In the second place, the navigation of a stream can only be estimated by its lowest depth recorded, and its horse power in the same way. But this same river, which in the autumn was only four feet deep and developed a corresponding horse power, would have an average depth of eight feet with four times the horse power. If then, the water that wastefully and ruinously flows down in the spring is conserved all through the summer, the river has been made more than four times as valuable."

"And how is this done?"

"That's too big a subject to take up now. Still, you can understand that if you dam the stream high up, and divert all the water over a certain height into immense reservoirs, the water could be let down gradually later. But that all depends on the measurement, which is taken daily for years, often--as in the case I was in--from a cable stretched from bank to bank, from which a little 'bos'un's chair' is hanging on a pulley, so that sitting in this little framework you can reach up to the cable and pull yourself to and fro. The one over the Susquehanna, where I was, is over a mile long, and of course it's pretty high up to allow for the sag, which is not small on a wire of that immense span."

Roger had a host of questions to ask but kept silent, not wanting to monopolize the talk when older men were there.

"By the way, Roberts," asked Field, seeking to change the subject from a topic which was stale to all the members of the party except Roger, "how did you like the work in the lower Sacramento Valley?"

"Parts of it weren't so bad, Mr. Field," was the reply. "Indeed, I think I've struck worse going right up here and in the Mud Lake district, but the project down there is on so large a scale that one is bound to become enthusiastic in the work. The bush is very dense, of course, semi-tropical in character, but where the growth is heavy the swamp is not so bad, so that it becomes a mere question of bushwhacking. Then, too, that southern stuff is all soft to cut and much easier to get through. The tule gra.s.s, however, is different."

"I've never been down in that tule gra.s.s," said one of the party, "is it as bad as has been described?"

"It's never been adequately described on paper," was the ready answer.

"Uncle Sam wouldn't let the report go through the mails."

Roger grinned.

"But what is it like, Mr. Roberts?" he said.

The newcomer thought for a moment.

"It's like what a field of wheat would seem to a very small dog," he answered. "It's too thick to walk through, too high to see over, and as stuffy as a tenement house with all the windows nailed down."

"How do you manage it then," asked the boy. "Do you go on stilts?"

"Stilts!" e.j.a.c.u.l.a.t.ed the surveyor. "You'd have to be an opera dancer with legs about twelve feet long to manage stilts down there. And even after you cut it down, walking on the stubble is like tramping over bayonet blades stuck in the ground point up. No, what we do is to cut a sort of trail for a horse, who is. .h.i.tched to a light buckboard. The horse goes through because he's got to, and the buckboard follows unless the harness breaks."

"But how do you get your tripods above the rushes," said the chief, "for you surely can't cut lines everywhere."

"We don't. The legs of the tripod are spliced to sticks long enough to raise them above the gra.s.s: and the topographer, standing sometimes on the body of the buckboard, sometimes on the seat, works with his nose just peering above the giant rushes, from a rod of extra length, deducting from his calculations the height of the tripod and the buckboard from the ground."

"And is it dry?"

"Mostly, except when the tide comes in at the lower part. At least, it's not soggy wet, like it is here. It's dead easy to get lost though, and you can't see any landmarks. You could chase your own back hair for a week and never know that you were going in a circle."

"Apropos of getting lost, Roberts," said the older man, "we had a little experience with the lad here that is worth repeating," and beginning from the snipe-hunt, he related the entire affair, showing first how well they had got the laugh on the tenderfoot, and how he had got back in return. Roberts laughed long and heartily at the picture conjured up of Roger sitting in the boughs above the party, hearing them discuss plans for his rescue and heroically resolving to leave nothing undone till they should find him.

[Ill.u.s.tration: DIFFICULTIES OF WORK.

In the Giant Tule Swamps in the Southern Sacramento Valley. The umbrella is not for comfort, but to keep the sun off the instrument.

_Photographs by U.S.G.S._]

"I didn't fare as well when I got trapped down there," he commented, "and while I suppose it was funny, I couldn't see the joke of it myself."

"Was that in the tule gra.s.s?" asked Field. "Tell us the yarn."

"I think I told you," began the new a.s.sistant, "how hard that stuff is to make a way through, and though it is really almost as tangled as this marsh work up here, the ground is so flat that far fewer bench marks are required. We had taken a long sight, because there was a sort of depression at that point which we wanted to delimit, and I was quite a distance from the plane table. Suddenly I felt a swish of water at my feet, my first realization that the tide was coming in. This had often happened before, and the water usually rose to a little above the knee, when, as soon as the tide ebbed, it would flow out and leave all dry again.

"Of course I was aware that I was working in a slight depression, but as a matter of fact it never occurred to me that this would make any especial difference. I was surprised, certainly, at the strength of the tide as it flowed in, and I remember a little later wondering whether it was spring tide and not being able to find any reason for the heavy flow, but it was only casually that the matter occurred to me at all.

Few minutes elapsed, however, before I realized that any greater increase of depth would be a really serious matter. The water was already above my knees and increasing at an alarming rate. I think I have shown you how hard it is to get through that stuff, and to cross a hundred yards of tule gra.s.s is a matter of half an hour's work. Still, at any moment, I thought the water would reach its maximum and I felt ashamed to start back after all the labor of reaching the point where I then was.

"Of course I am not usually the tallest man in the party [the speaker was not more than five feet six or seven] and the boys used to joke me about my height. I knew they would roast me to a turn if I had to let on that I was afraid of being drowned in a few feet of water. So I held on. But the water had crept up rapidly until it was well above my waist, and I determined, jesting or no jesting, that I was going to strike for higher ground, or, if possible, get as far as the buckboard. The other fellows couldn't see the trouble I was in because they were on a little crest of ground, and because the waving tule gra.s.s shut off all sight of the water.