"Well, that won't help us much," said Inspector Burton, disappointedly.
"We know, of course, that it is bound to be in the southern part of the state, probably even below Los Angeles, in order that the coolie boats can make their run from Mexico in one night."
"I see," said Jack, composedly. "But that wasn't the only thing I had in mind."
"What else?"
"Let an expert at solving codes listen in when once the code conversations are picked up. He can take down what he hears. The probability is he can work out a solution. To a genuine expert, as I understand it, there is no code that cannot be solved."
"But," objected Mr. Temple, "the code picked up and deciphered might be from some station like yours, Jack."
"In which case you mean it would be about legitimate business?" said Jack. "But the government will have licensed stations listed, and their codes on file. No, I believe it would be a good move to put a code expert at work at the Los Angeles station."
"So do I," said Inspector Burton, warmly. "I want to thank you. And I want to thank you, too," he added, turning to Frank. "Your information will undoubtedly prove to be of the very greatest value."
He rose.
"I shall have to go now," he said. "I suppose you all will be viewing the city and taking in the sights. I wish I could stay to show it to you. But that cannot be. What you have told me makes it necessary for me to leave at once for the south. I shall arrange my affairs here and take the night train to Los Angeles. I may not see you again. But I know you will be interested in the outcome and"-turning to Mr. Temple-"if you give me your address I promise to let you know."
Mr. Temple took out a business card and handed it to the other. Then he accompanied him to the door.
"Good-bye," called the chums, in chorus. "Good luck."
"Well," said Bob, when his father returned, "that's that. Now, Dad, you will want to attend to your business affairs today. What do you suggest we do?"
"Hire a car," said his father, promptly, "and drive around the city. Be back here at five. Then we'll dress and have dinner in one of the city's famous restaurants. San Francisco is noted for its wonderful dining places. Afterward, we can all go to a theatre or just walk around and view the city at night."
CHAPTER V
THE SOUND DETECTOR
"Where to, first?" queried Frank. "I vote for the Cliff House and Seal Rocks. Here in the guide book it says 'the seals play sportively in the restless tide.' And Sutro Baths are nearby, too, I gather-the largest indoor salt water pool in the world."
All three chums stood on the Market Street sidewalk before the Palace Hotel. The hour was near eleven. The usual early morning fog which had hung over the city, as it does practically every day of the year, had been dissipated for an hour or more. The sky was cloudless and blue, the sunshine brilliant. A brisk breeze blew along the tremendously wide thoroughfare, which is the widest of all the great city streets of the land, so wide, in fact, that it accommodates four street car lines with the width of an ordinary street left over on each side between the outer tracks and the curbs.
"How delightfully cool and exhilarating!" commented big Bob, drawing in and expelling great lungfuls of the crisp air. "I haven't felt so peppy in days."
"The guide book says that's the San Francisco climate," said Frank.
"Cool, snappy days all the year round."
"Your car, sir," said a uniformed doorman to Jack.
They looked up to find a handsome limousine drawn to the curb. This was the car they had ordered for the day. The boys moved toward it.
"We ought to decide right now where we want to go," declared Frank.
Jack had an inspiration.
"I'll tell you what, fellows," he said. "Father gave me the name and address of a man who invented some new radio equipment, and advised me to look him up. Suppose we do that, first. Then we can go sightseeing.
It just occurred to me. Wonder where that address is."
He began leafing over the pages of a small memorandum book.
"Here it is. Bender, Silas Bender. 1453 Mission Street. Let's ask the chauffeur how far away that is."
After a little discussion, it developed the address given-on the first street paralleling Market to the south-lay on the route to Golden Gate Park, the Cliff House and Seal Rocks, whither the boys wanted to go.
Accordingly, all piled into the car and sped away.
Mr. Bender maintained a little equipment store supplying radio apparatus. The shop was empty of customers when the boys arrived, and, at the ringing of the bell on their entrance, a medium-sized man, brisk and alert, came from the rear room outfitted as workshop. His thinning hair was rumpled. He was in his shirt sleeves.
"What can I do for you, gentlemen?" he asked inquiringly.
Jack stepped forward.
"Are you Mr. Bender?"
"I am."
"Well, I'm Jack Hampton," said Jack, extending his hand. "Here's a note from my father. I believe you have met him."
"Mr. Hampton the engineer?"
Jack nodded.
"Say, I am glad to meet you," said Mr. Bender enthusiastically. "Yes. I know your father. When he was on the Coast some years ago on his way to Alaska I met him. He's enthusiastic about radio telephony. We had a number of very pleasant talks. I remember him very well. But here, I'm keeping you standing. Won't you come back into my workshop and sit down.
Bring your friends."
Jack accomplished the necessary introductions, and they followed Mr.
Bender into the room in the rear.
For a time the boys were kept busy examining various radio appliances, which the energetic Mr. Bender kept thrusting at them. All the time he kept up a running fire of comment.
"Now this," he said, taking up a small device of unusual shape, "is a sound detector. The only similar device in the field so far is the radio compass, but it is clumsy and unreliable. With this device, however, I am quite certain I have solved the problem of locating the point of origin of any strange or unusual sounds in the air."
Jack gave an exclamation.
"What say?" asked Mr. Bender, turning toward him.
Jack could hardly conceal his impatience.
"How does it work?" he asked eagerly.
"Well, suppose we wanted to locate the point of origin of some strange message heard at the radio station out at Golden Gate Park. First, we would use a sound detector there, and find out along what line the strange sound came to the station. It might be up the coast or down, or east, southeast or northeast. Suppose it came from down the coast, or south. Then, at a point southeast of this city, we would again apply the sound detector and again at a third point south of the second. When at all three stations, the strange sound was loudest, we would have three bearings upon the point of its origin. Where they intersected, the--"
"The smuggler's cove would be located," said Frank quick-tongued.