The Radio Boys on Secret Service Duty

  CHAPTER V

  THE SOUND DETECTOR

  "Where to, first?" queried Frank. "I vote for the Cliff House and SealRocks. Here in the guide book it says 'the seals play sportively in therestless tide.' And Sutro Baths are nearby, too, I gather--the largestindoor salt water pool in the world."

  All three chums stood on the Market Street sidewalk before the PalaceHotel. The hour was near eleven. The usual early morning fog which hadhung over the city, as it does practically every day of the year, hadbeen dissipated for an hour or more. The sky was cloudless and blue, thesunshine brilliant. A brisk breeze blew along the tremendously widethoroughfare, which is the widest of all the great city streets of theland, so wide, in fact, that it accommodates four street car lines withthe width of an ordinary street left over on each side between the outertracks and the curbs.

  "How delightfully cool and exhilarating!" commented big Bob, drawing inand expelling great lungfuls of the crisp air. "I haven't felt so peppyin 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 wasthe 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 andaddress of a man who invented some new radio equipment, and advised meto 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 thechauffeur how far away that is."

  After a little discussion, it developed the address given--on the firststreet paralleling Market to the south--lay on the route to Golden GatePark, 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 radioapparatus. The shop was empty of customers when the boys arrived, and,at the ringing of the bell on their entrance, a medium-sized man, briskand alert, came from the rear room outfitted as workshop. His thinninghair 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 notefrom 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. Iknow your father. When he was on the Coast some years ago on his way toAlaska I met him. He's enthusiastic about radio telephony. We had anumber of very pleasant talks. I remember him very well. But here, I'mkeeping 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 hekept up a running fire of comment.

  "Now this," he said, taking up a small device of unusual shape, "is asound detector. The only similar device in the field so far is the radiocompass, but it is clumsy and unreliable. With this device, however, Iam quite certain I have solved the problem of locating the point oforigin 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 strangemessage heard at the radio station out at Golden Gate Park. First, wewould use a sound detector there, and find out along what line thestrange sound came to the station. It might be up the coast or down, oreast, southeast or northeast. Suppose it came from down the coast, orsouth. Then, at a point southeast of this city, we would again apply thesound detector and again at a third point south of the second. When atall three stations, the strange sound was loudest, we would have threebearings upon the point of its origin. Where they intersected, the----"

  "The smuggler's cove would be located," said Frank quick-tongued.

  The next moment he was covered with confusion as Mr. Bender regarded himblankly. So intent had the inventor been upon the description of hisdevice and the method of its operation that he was aware only of aninterruption but did not realize the nature of it.

  Jack and Bob glared at Frank.

  "Eh?" said Mr. Bender. "What say?"

  "I just said something about the point of origin being where the linesintersected," declared Frank, considering it wise to withhold the wholetruth, inasmuch as the matter of the smugglers was not his to divulge.

  "Yes, certainly," said Mr. Bender, abstractedly. "Yes, project imaginarylines from each station and where they intersect will be the station youare hunting."

  Abruptly he put aside the sound detector as if, now that he hadexplained its operation, it were of no more value.

  "Here," he said, taking up a suitcase, and swinging it around, "is aradio receiving device that can be carried easily in this smallsuitcase. And here"--putting down the suitcase before the boys couldexamine it and taking up a finger ring from a workbench--"is the smallestreceiving set I have yet devised. It is, as you see, in the shape of aring and can be worn without the presence of the device beingsuspected."

  "Mr. Bender," said Frank, "will you excuse my friends and me for a fewmoments while we step aside and have a little confab. I believe we willhave a proposal to make that will interest you."

  "I know what you mean," said Frank, as Mr. Bender withdrew, leaving themalone. "That sound detector, hey? If the Secret Service man had that hewould be able to locate the smuggler's cove."

  "That's it, exactly," said Jack. "Inspector Burton said he would not beleaving for Los Angeles until tonight. I believe we ought to get hold ofhim at once and tell him about this possibility."

  "I'm with you," said Bob. "But we don't know how to reach him. Suppose Icall Father at the office of his business representative, and ask him toget Inspector Burton."

  "Good idea," said Jack. "I didn't know just how to work it. But if yourfather gets Inspector Burton to come up here, we will not be revealinganything to Mr. Bender, and the inspector can tell as much or little ashe wants."

  "Then I'll telephone father," said Bob. "I saw a telephone in the storewhen we came in. I suppose Mr. Bender will let me use it."

  "And I'll explain as much as necessary to Mr. Bender," said Jack.

  Accordingly, he called the inventor back to the workroom while Bobtelephoned Mr. Temple, and explained they were inviting a man to come upand talk to him about the sound detector.

  "I can't tell you any more than that now, Mr. Bender," said Jack. "But Ipromise you, of course, that your invention is not in any danger ofbeing stolen. On the contrary, the man we have asked to come here mayput you in the way of making your fortune."