The notion that Chemistry could be a true example of Natural Philosophy was initiated by virtuosi such as Robert Boyle and Isaac Newton in the 17th century. The 19th century was the great age of Natural Philosophy and one of the best examples of this genre was the Preliminary Discourse on the Study of Natural Philosophy (1851) by Sir John F.W. Herschel, Bart. K.H. (1792-1871). Although he was one of the greatest astronomers of all time, his ability to carefully examine real data and to discern patterns also helped him reach conclusions in chemistry that remain true today. By the middle of the 19th century, there were between 50 and 60 elements acknowledged by the world of chemistry. It was already known that the chemical properties of distinct groups of elements were similar. Herschel was also a celebrated mineralogist, and he observed that certain elements formed salts with crystal forms that were similar, a result proposed by Mitscherlich. Herschel accepted the Daltonian notion that crystals were composed of atoms located on a lattice. The law of isomorphism (similarity) is one of the notions that support the paradigm of periodicity. Herschel believed that Chemistry should be founded on the best data, and insisted that fellow chemists establish precise values for elemental properties like atomic weight. But, as a Natural Philosopher, he valued bold speculative conclusions, as long as they were thoroughly tested by actual data. Each substance required detailed quantitative characterization. For Sir John Herschel, science was hard work, but well worth the effort when properly conducted. He was the President of the Chemistry Section of the British Association for the Advancement of Science in 1858 and delivered the plenary address that year. He cited Josiah Parsons Cooke of Harvard University as his inspiration for recognizing the chemical organizing principle for the elements. This had been presented in 1854 and published in the Memoirs of the American Academy of Arts and Sciences in 1855. While Cooke was still working with a bad set of atomic weights and he did not know the correct empirical formulae for many compounds, he did organize the elements into groups that had similar chemistry. C.S. Peirce, the Harvard polymath, argued for recognition of the work of Cooke in 1892. There was still much work to be done in 1858 when Herschel praised the work of Cooke, but a major step had been taken.

Sir John F.W. Herschel and the concept of periodicity

2019 Fall National Meeting

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