After scientists have done an experiment or a series of experiments, they usually take time to write their reports. This not only gives them a chance to get their thinking together but also—and even more important—enables them to share their work with other scientists. They explain their results and also present persuasive arguments in favor of their conclusions. This chapter references and shares the beginning of a handwritten letter from Issac Newton on an experiment he did on the colors produced by a prism.