The cave, so graphically described in Tom Sawyer, was one of Sam's favourite haunts; and his first sweetheart was Laura Hawkins, the Becky Thatcher of Tom's admiration. “Sam was always up to some mischief,” this lady once remarked in later life, when in reminiscential mood. “We attended Sunday-school together, and they had a system of rewards for saying verses after committing them to memory. A blue ticket was given for ten verses, a red ticket for ten blue, a yellow for ten red, and a Bible for ten yellow tickets. If you will count up, you will see it makes a Bible for ten thousand verses. Sam came up one day with his ten yellow tickets, and everybody knew he had not said a verse, but had just got them by trading with the boys. But he received his Bible with all the serious air of a diligent student!” Mark Twain, save when in humorous vein, has never pretended that his success was due to any marvellous qualities of mind, any indefatigable industry, any innate energy and perseverance. I have good reason to recall his favourite theory, which he was fond of expounding, to the effect that circumstance is man's master. He likened circumstance to the attraction of gravity; and declared that while it is man's privilege to argue with circumstance, as it is the honourable privilege of the falling body to argue with the attraction of gravity, it does no good: man has to obey. Circumstance has as its working partner man's temperament, his natural disposition. Temperament is not the creation of man, but an innate quality; over it he has no authority; for its acts he cannot be held responsible. It cannot be permanently changed or even modified. No power can keep it modified. For it is inherent and enduring, as unchanging as the lines upon the thumb or the conformation of the skull. Throughout his life, circumstance seemed like a watchful spirit, switching his temperament into those channels of experience and development leading unerringly to the career of the author.