no 



NATURE 



[April io, 1919 



of his own discovery relating- to attraction and 

 repulsion accompanying' radiation, and in 1873 

 he astonished the world by the invention of the 

 radiometer. Probably no discovery within our 

 time has given rise to more speculation or has led 

 to a more remarkable development of ideas con- 

 nected with radiation, and though Crookes did 

 not furnish the true explanation of his instrument, 

 he contributed a large number of experiments 

 which assisted in its ultimate recognition. 



From the phenomena shown by the radiometer 

 was an easy step to the study of electrical dis- 

 charges in high vacua, and henceforward his work 

 on what he called "radiant matter " furnished the 

 starting-point for many of the famous discoveries 

 by others which have led to a completely new 

 field of physics and an utterly novel view of the 

 ultimate constitution of matter. Crookes 's study 

 of the rays from the cathode in a vacuum tube in 

 which the gas was rarefied beyond a certain limit 

 led him to consider that the flying particles repre- 

 sented an ultra-gaseous condition which he re- 

 garded as a fourth state of matter. This view, 

 which at the time was rather unfavourably re- 

 ceived, has been completely justified by further 

 investigations, though his idea of the mass of the 

 radiant particles has had to be modified. 



About 1885 Crookes became interested in the 

 phosphorescent spectra of solid bodies, and espe- 

 cially injlhose of the so-called rare earths. This 

 led him to engage in very lengthy series of ex- 

 periments on fractionation, and attempts at the 

 resolution of mixtures of these substances into 

 their constituents, and so he was led into the 

 conception of what he called meta-elements. He 

 supposed that some oxides, like yttria, might 

 consist of molecules so nearly alike in properties 

 and mass as to be indistinguishable from one 

 another, and inseparable by any known process. 

 Accordingly, these substances were represented 

 in the periodic scheme of the elements as cluster- 

 ing into groups near to certain values of atomic 

 weights. Crookes also devised a spiral model 

 which has become very familiar for displaying 

 the relations of the elements to atomic weight in 

 connection with the periodic law and for illus- 

 trating his own views as to the "genesis of the 

 elements." The definition of the term "element " 

 in chemistry, and the characterisation of the 

 recognised elements, formed the subject of his 

 two presidential addresses to the Chemical 

 Society in 1888 and 1889. 



During the subsequent thirty years of his life 

 Crookes was much occupied with further experi- 

 ;mental work on questions cognate to these 

 subjects. His familiarity ' with spectroscopy 

 enabled him to pursue successfully an inquiry into 

 the preparation of eye-preserving glass for spec- 

 tacles, the results of which were published in the 

 Philosophical Transactions so recently as 1914, 

 and have led to valuable practical results, espe- 

 cially in the case of workers in glass and others 

 exposed to furnace glare. The primary object 

 was to find a glass which will cut off as much as 

 possible of the heat radiation, but the experiments 



NO. 2580, VOL. 103] 



were extended to the search for glasses opaque to 

 the ultraviolet. More than three hundred different 

 glasses were investigated, and the compositions 

 of nineteen which have been proved useful are 

 given in the memoir. 



It would be impossible in the short space at 

 ■our disposal now to complete the list of Sir 

 William Crookes's various spheres of activity, 

 but mention must not be omitted of some of his 

 publications. In 1859 he started the Chemical 

 News, of which he continued to be proprietor and 

 editor to the end of his life. His famous British 

 Association address at Bristol in 1899 on "The 

 Wheat Problem " attracted for many years con- 

 siderable attention from economists and agricul- 

 turists, arfd his visits to South Africa in 1896 and 

 in 1905 led to the publication of a small work on 

 diamonds, which has had a large circulation. To 

 these may be added the volume entitled " Select 

 Methods in Chemical Analysis," which is full of 

 useful information, and has passed through four 

 editions, as well as several other books of a 

 technical character. 



Crookes was a man of extraordinary genius 

 and immense physical activity, of which his 

 copious published work is evidence. A man of 

 his temperament and his remarkable independence 

 of view in regard to the range of scientific inquiry 

 and the proper attitude of the scientific investi- 

 gator would naturally be led to look attentively 

 at subjects of all kinds, some of which might be 

 regarded as suspect by other people. It is, of 

 .course, well known that he took part in many 

 .inquiries concerning psychic phenomena, and 

 that he published a book on spiritualism, in which 

 he recorded certain experiences of his own. 

 These, however, are subjects on which there is 

 itoo much difference of sentiment and of opinion 

 ito be further considered now ; they must be left 

 to be handled by the biographer. All that the 

 scientific world now feels is that it has lost a 

 gieat pioneer worker in the field of natural know- 

 ledge. 



It is needless to add that honours of all kinds 

 fell thick on Crooke^. He was elected into the 

 iRoyal Society in 1863, and the Royal, the Davy, 

 and the Copley medals were awarded to him by 

 the society, of which he finally became president. 

 He also served as president of several other 

 societies, including the Chemical Society, the 

 British Association, and the Institution of Elec- 

 trical Engineers. He received a gold medal and a 

 prize of 6000 francs from the French Academy of 

 Sciences in 1880, and in 1899 the Albert medal 

 of the Royal Society of Arts was awarded to him. 

 The Order of Merit was conferred on him in 1910. 



It may be of interest to some readers of 

 jNature to be reminded that in the series of 

 "Scientific Worthies" issued by this journal was 

 ipublished on November 7, 1907, an appreciation 

 of Crookes's scientific work from the pen of a 

 distinguished physicist. Prof. P. Zeeman, of 

 Amsterdam, which affords an estimate of the 

 value of his work by a highly competerft authority. 



W. A. T. 



