In his only known historical sketch addressing the origin of the chemical atomic theory, John Dalton stated that different atoms have different sizes, a conclusion which led him to an investigation of combining number of atoms and relative weights. Although he stated the idea occurred to him in 1805, his laboratory notes show he developed the first table of atomic weights in 1803. Historians over the years have provided conflicting narratives to explain the different dates. In this paper, I examine Dalton’s activities as a creative individual and a practicing chemist, arguing that Dalton’s concept of atomic size was not an “aha” moment occurring in 1805, but one that he used right from the start in 1803 to develop his chemical atomic theory. The concepts of atomic size and relative atomic weights emerged in 1803 from his investigations into caloric and the composition of nitric acid, respectively, not from his studies on gaseous solubility. In 1805, Dalton applied his 1803 concept of atomic size to explain a different problem, one of gaseous diffusion. Dalton’s 1805 epiphany should join the stage with other great insights in the history of science, such as those of Archimedes, Kekulé, and Poincaré.

约翰·道尔顿（John Dalton）在他唯一的有关化学原子理论起源的历史草图中指出，不同的原子具有不同的大小，这一结论使他开始研究结合原子数和相对重量。尽管他说这个主意是在1805年发生的，但是他的实验室笔记显示他在1803年开发了第一张原子量表。多年来的历史学家提供了相互矛盾的叙述来解释不同的日期。在本文中，我检查了道尔顿作为一个有创造力的个人和一名化学工作者的活动，认为道尔顿的原子尺寸概念不是在1805年发生的“ aha”时刻，而是他从1803年开始就使用的用于发展其化学物质的那个时刻。原子理论。原子大小和相对原子量的概念起源于1803年，分别是他对热量和硝酸成分的研究，而不是他对气体溶解度的研究。1805年，道尔顿运用他的1803年原子尺寸概念来解释一个不同的问题，即气体扩散。道尔顿1805年的顿悟应该与科学史上的其他伟大见解（例如阿基米德，凯库莱和庞加莱的观点）一起登上舞台。