Agamemnon was delayed, however, in his choice of a profession, by a desire he had to become a famous inventor. If he could only invent something important, and get out a patent, he would make himself known all over the country. If he could get out a patent he would be set up for life, or at least as long as the patent lasted, and it would be well to be sure to arrange it to last through his natural life. Indeed, he had gone so far as to make his invention. It had been suggested by their trouble with a key, in their late moving to their new house. He had studied the matter over a great deal. He looked it up in the Encyclopaedia, and had spent a day or two in the Public Library, in reading about Chubb's Lock and other patent locks. But his plan was more simple. It was this: that all keys should be made alike! He wondered it had not been thought of before; but so it was, Solomon John said, with all inventions, with Christopher Columbus, and everybody. Nobody knew the invention till it was invented, and then it looked very simple. With Agamemnon's plan you need have but one key, that should fit everything! It should be a medium-sized key, not too large to carry. It ought to answer for a house door, but you might open a portmanteau with it. How much less danger there would be of losing one's keys if there were only one to lose! [Illustration] Mrs. Peterkin thought it would be inconvenient if their father were out, and she wanted to open the jam-closet for the little boys. But Agamemnon explained that he did not mean there should be but one key in the family, or an a town,--you might have as many as you pleased, only they should all be alike. [Illustration] Elizabeth Eliza felt it would be a great convenience,--they could keep the front door always locked, yet she could open it with the key of her upper drawer; that she was sure to have with her. And Mrs. Peterkin felt it might be a convenience if they had one on each story, so that they need not go up and down for it. Mr. Peterkin studied all the papers and advertisements, to decide about the lawyer whom they should consult, and at last, one morning, they went into town to visit a patent-agent. Elizabeth Eliza took the occasion to make a call upon the lady from Philadelphia, but she came back hurriedly to her mother. "I have had a delightful call," she said; "but--perhaps I was wrong--I could not help, in conversation, speaking of Agamemnon's proposed patent. I ought not to have mentioned it, as such things are kept profound secrets; they say women always do tell things; I suppose that is the reason." "But where is the harm?" asked Mrs. Peterkin. "I'm sure you can trust the lady from Philadelphia." Elizabeth Eliza then explained that the lady from Philadelphia had questioned the plan a little when it was told her, and had suggested that "if everybody had the same key there would be no particular use in a lock." [Illustration]