Mr. Hampton, Bob and Frank nodded sympathetically. An enthusiast on radio, Jack had developed a number of new appliances. The latest of these was not yet completed. He had worked on it in the laboratories at Yale during the Winter and Spring. The lateness of his return to his classes, however, inasmuch as he did not arrive at college until after Christmas, due to the delay occasioned by his adventures in South America in search of "The Enchanted City of the Incas," compelled him to devote most his time to catching up in his studies. He did not, therefore, have as much time to devote to laboratory experiments as he desired. As a consequence, the 20-kilowatt tube had not yet been perfected, when time came for him to depart for Alaska with his father.

Jack's 20-kilowatt tube, when completed, would be the most powerful in the world, and he expected, moreover, to construct others of greater kilo-wattage. A 75-kilowatt tube had been produced in England, it is true, but it had not been found practicable. Jack's tube was to be steel-jacketed and equipped with a water-cooling device, due to the heat produced when in operation. His big dream was that this tube, when used as an amplifier in conjunction with an alternator, would make trans-atlantic telephonic communication as common as cabling or wireless telegraphing.

"If I only had one of my 20-kilowatt tubes now," he mourned, "we would be able to talk not only with Mr. MacDonald's Post but with Dawson or even Nome."

"Well, Jack," said Frank, "it's too bad. Just the same, let's get busy. For, with our 50-watt oscillator tube set we will be able to communicate by telegraph up to 500 miles. And, as the Post is only 400 miles away, we can reach it easily."

For sending up to 500 miles, the boys knew they could use either three or four 5-watt oscillator tubes in parallel, or one 50-watt oscillator tube. They had decided on the latter method, in making their preparations for departure in faraway Seattle. For one thing, and the biggest, transportation was the most important item. And the 50-watt tube set was the more compact. Quickly, then, with Mr. Hampton helping, they got out the various parts from their baggage and made the connections.

Farnum, the Northwest policeman, MacDonald, and Dick and Art, watched with puzzled interest and even awe as the four, working in unison, put together the aerial series condenser, the blocking condenser, the grid condenser, the telegraph key, the chopper, the choke coil in the key circuit, the filament volt-meter, the protective condenser in the power circuit, the storage battery and the motor generator.

Farnum and MacDonald asked questions, although Dick and Art were content to sit silent and watch, keen-eyed, as the construction work progressed. Several times, too, Dick arose and went to the water's edge to keep watch against surprise. That any would be attempted for the time being, nobody believed, as they figured the enemy would consider them on guard.

As they worked, Jack explained for the benefit of the others. His description of how the low voltage current from the storage battery flowed into one of the windings of the generator and drives it as a motor thus generating higher voltage in the other winding both puzzled and interested them. By the time, the set was ready for use, Farnum, who was something of a mechanic by inclination, had a fair understanding of the set, but MacDonald, though interested, was bewildered.

"I'm fair beat," he confessed. "Anyhow, just so you boys can make it work!"

"Oh, we'll make it work, all right," Frank assured him. "Well, now, to try to call the Post. What's its call, Mr. MacDonald?"

"I happen to remember," said MacDonald. "We were all so interested when wireless was put in that Captain Jameson gave us a little lecture on it. He said our call would be JSN, abbreviation for his name. We were to remember it, in case of need, when we were able to get to a wireless station. Well, this is a case of need."

"I'll say it is," said big Bob. "Well, come on, fellows, who's going to call?"

It was an honor or distinction that each was eager to have, yet each wanted to force it on the others. A friendly argument developed, to which Mr. Hampton, smiling, put an end.

"Look here, boys, we are wasting time. Suppose you draw straws for the privilege. You all know the Morse and Continental codes, so there is no question of ability involved. Here-" breaking three matchsticks into varying lengths and offering them-"take your choice. Longest wins."

Frank drew the winning stick. The others laughed, clapped him on the back, and without more ado he began pressing the key and sending out the signal.

"Is somebody on duty at the Post wireless station, do you think, MacDonald?" asked Mr. Hampton.

"Somebody there all the time," the latter replied. "Captain Jameson has found wireless so useful in policing his vast district that he wonders how he ever got along without it."

"Hurray," shouted Frank, "listen. They're answering."

To those who understood the code, the answer was plain:

"JSN answering. Who are you?"

"MacDonald," tapped off Frank, grinning mischievously.

The receptor sounded almost angry.

"Quit your kidding."

"No, I mean it," replied Frank. "This is MacDonald of the Mounted."

"Prove it."

"That'll stump old Frank," chuckled Bob, in an aside. But he was mistaken.

"All right," replied Frank, confidently. "Do you know what my assignment is?"

"Yes," answered JSN, impudently. "Do you?"

"I'm after Lupo the Wolf," tapped Frank. "Now call Captain Jameson."

"You're not MacDonald," replied JSN, "because he doesn't know the code. But you must be speaking for him, for that's right about his assignment. I'll call Captain Jameson. You wait."

"All right," tapped Frank.

Then he turned to the eager MacDonald, who was itching to inquire what was occurring, but had restrained himself until he should be appealed to by Frank, in order not to interrupt. Like all men unfamiliar with telegraphy, whether wireless or by wire, he stood in awe of an operator, and believed it would be terrible, indeed, to interrupt that superior being. Frank took pity now on his curiosity, as well as on that of Farnum, Dick and Art, crowding behind him, and explained what had happened.

"And you actually got the Post?" asked MacDonald, doubt in his voice.

Frank nodded.

"My God," said the big policeman. "Think of the weeks I spent toiling up here, and now you come along and talk across that distance without the loss of a minute's time. Wonderful, well I reckon."

"When Captain Jameson arrives," said Frank, smiling, "I want you to stand close and I'll translate what he says, and you help me with the replies, will you?"

"Won't I be interrupting you?"

"Oh, no," smiled Frank. "You just come close and wait until I speak. It'll be all right. Well"-as the receptor began to click-"I guess this is Captain Jameson now. Yes," with a nod, "it's he, all right. He's asking where you are, Mr. MacDonald."

"Tell him I'm four hundred miles away and close on Lupo. Tell him about yourselves and the fight, and that we're going to round up Lupo's gang and ask him how soon he can send men to help me out with any prisoners we take, and if he can send any at all, and-"

"One minute," said Frank. "I understand. Just wait a bit now, while I telegraph."

To explain at length the details of that telegraphic conversation is unnecessary. Suffice it to say, that the situation was fully explained to Captain Jameson, and that the latter agreed to start a half dozen deputies under a Sergeant to MacDonald's aid, as soon as he should hear again as to the outcome of the expedition against Lupo.

"It'll take a while for the men to reach MacDonald," said Captain Jameson. "But with game plentiful and the season open, he can camp until they arrive, and thus keep watch over his prisoners, providing he makes any. You people go ahead with your rounding up of Lupo's gang, and then let me hear from you again."

On that agreement, Frank finally closed the conversation, as there was nothing further to be said.

Chapter 9 -A CALL TO THE FORT.

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