The hope of financial reward stimulates enterprisers, as we have seen, to exert themselves industrially. The same hope stimulates inventions and literary productions, though the opinion prevails among many people that inventors and authors work merely for the love of the work itself. Occasionally some individual gives his whole life unselfishly to the production of a machine, or to the discovery of a chemical process, or to the writing of a book. The overwhelming majority of men, however, whether they be enterprisers, laborers, scientists, or authors, are encouraged, if not inspired, to toil long hours and to undergo mental and physical discomfort by the hope that their labors will bring them financial reward. And it is fortunate for the progress of the industrial arts that men are willing to think and to work, even though they are prompted wholly or in part by selfish motives. Realizing that a hope of financial reward serves to encourage inventive genius, the United States in common with all other civilized nations permits inventors and authors to enjoy a monopoly of their products. Practices vary from country to country, though the principle involved is the same in all cases.