views on the nature of ‘radiant matter’ proved to be mistaken. He believed the rays to consist of streams of particles of ordinary molecular magnitude. It remained for (Sir) J. J. Thomson to discover their subatomic nature, and to prove that cathode rays consist of streams of negative electrons, that is, of negatively electrified particles whose mass is only 1/1,800 that of the atom of hydrogen. Nevertheless, Crookes’s experimental work in this field was the foundation of discoveries which have changed the whole conception of chemistry and physics. Moreover, it is characteristic of him that, though already advanced in years, he readily and enthusiastically accepted the new interpretation of his work.
For many years Crookes conducted laborious experiments on the elements of the rare earths, elements so similar to one another in chemical properties that special methods for their separation had to be devised. Throughout the work he employed spectroscopic methods for following the course, and testing the completeness, of the separation of one element from another. What had been one of the most obscure regions in inorganic chemistry gradually became clear. In the course of the years during which he was thus occupied, Crookes was led to views on the existence of ‘meta-elements’, or clusters of elements resembling one another so closely that in most ways the cluster behaves as a single individual. The ‘meta-elements’ of Crookes bear a superficial resemblance to the mixtures of isotopes of which some elements are now known to consist; but the theory of meta-elements cannot justly be said to anticipate the discovery of isotopes, since it was based upon facts of a fundamentally different kind from those on which more recent views on isotopic elements are founded.
Turning his attention to the newly discovered phenomena of radio-activity, Crookes, in 1900, achieved the separation from uranium of its active transformation product, uranium-X. He observed the gradual decay of the separated transformation product, and the simultaneous reproduction of a fresh supply in the original uranium. At about the same time as this important discovery, he observed that when ‘a-particles’, ejected from radio-active substances, impinge upon zinc sulphide, each impact is accompanied by a minute scintillation, an observation which forms the basis of one of the most useful methods in the technique of radio-activity.
Crookes published numerous papers on spectroscopy, a subject which always had a great fascination for him, and he made researches on a large variety of minor subjects. In addition to various technical books, he wrote a standard treatise on Select Methods in Chemical Analysis (1871), and a small book on Diamonds (1909), a subject to which he had devoted some study during two visits to South Africa. He frequently served the government in an advisory capacity, and his work on the production of a glass which should cut off from molten glass the rays which are injurious to the eyes of the work-people, may be cited among his many public services.
Sir William Crookes was a great experimenter. His material discoveries are of lasting and fundamental value, though his theoretical speculations have not stood the test of time so well. While it is true that all scientific theories serve primarily only for the suggestion of further research, it must be admitted that Crookes’s analytical power hardly equalled his gift as an investigator of new facts. His excursions into psychical research have been strongly criticized, and they certainly led him into some very curious situations, but they show that he thought all phenomena worthy of investigation, and refused to be bound by tradition and convention. He was a man of science in the broadest sense, an influential personality, and a doyen of his profession.
There is a portrait of Crookes by E. A. Walton in the rooms of the Royal Society, and another by P. Ludovici in the National Portrait Gallery.
[Proceedings of the Royal Society, vol. xcvi, A, 1919-1920 (portrait); P. Zeemann, Scientific Worthies, Sir William Crookes, in Nature, 7 November 1907; E. E. Fournier D’Albe, Life of Sir William Crookes, 1928; Crookes’s own papers and addresses in Transactions of the Chemical Society and Proceedings of the Royal Society.]
CROOKS, WILLIAM (1852-1921), labour politician, was born in Poplar 6 April 1852. His parents were very poor, his father having become a cripple, and at the age of eight Crooks, who had been already at work as a milkman’s boy, was sent to the workhouse, and later to the Poor Law school at Sutton, Surrey, where he was separated from all his family. This period left an enduring impression on his mind. When his parents were able to resume charge of him, he became first a grocer’s boy and then, at eleven years of age, labourer in a blacksmith’s shop. At
137
