Tom Swift and His Giant Cannon; Or, The Longest Shots on Record

Now, see here, Mr. Swift, you may think it all a sort of dream, and imagine that I don't know what I'm talking about; but I do! If you'll consent to finance this expedition to the extent of, say, ten thousand dollars, I'll practically guarantee to give you back five times that sum.
I don't know, Alec, I don't know, slowly responded the aged inventor. I've heard those stories before, and in my experience nothing ever came of them. Buried treasure, and lost vessels filled with gold, are all well and good, but hunting for an opal mine on some little-heard-of island goes them one better.
Then you don't feel like backing me up in this matter, Mr. Swift?
No, Alec, I can't say I do. Why, just stop and think for a minute. You're asking me to put ten thousand dollars into a company, to fit out an expedition to go to this island—somewhere down near Panama, you say it is—and try to locate the lost mine from which, some centuries ago, opals and other precious stones came. It doesn't seem reasonable.
But I'm sure I can find the mine, Mr. Swift! persisted Alec Peterson, who was almost as elderly a man as the one he addressed. I have the old documents that tell how rich the mine once was, how the old Mexican rulers used to get their opals from it, and how all trace of it was lost in the last century. I have all the landmarks down pat, and I'm sure I can find it. Come on now, take a chance. Put in this ten thousand dollars. I can manage the rest. You'll get back more than five times your investment.
If you find the mine—yes.
I tell you I will find it! Come now, Mr. Swift, and the visitor's voice was very pleading, you and your son Tom have made a fortune for yourselves out of your different inventions. Be generous, and lend me this ten thousand dollars.
Mr. Swift shook his head.
I've heard you talk the same way before, Alec, he replied. None of your schemes ever amounted to anything. You've been a fortune-hunter all your life, nearly; and what have you gotten out of it? Just a bare living.