Sir William Crookes 1832-1919

Sir William Crookes, O.M., F.R.S., born in London on 17 June 1832 is most noted for his discovery of thallium and his research in cathode rays.

His scientific career began in 1848 at the age of fifteen when he entered the Royal College of Chemistry, London, under A.W. von Hofmann. From 1850 to 1854 he became an assistant in the college and undertook his own work including research in spectroscopy. His first published papers in 1851 were on the subject of selenocyanides, new compounds of the element selenium. 

In 1854 he became Superintendent of the Meteorological Department at the Radcliffe Observatory, Oxford and in 1855 was appointed lecturer at the Chester College of Science. In 1859 he founded the Chemical News which he edited until 1906. After 1880 he lived in Kensington Park Gardens, London, where he built and equipped his own laboratory in order to devote his life to his research.


Crookes’ first great discovery was that of the element thallium in 1861. With this, his reputation had been established and he was elected a Fellow of the Royal Society in 1863. After years of research, he determined the atomic weight of the new element in observations that serve as an exemplar of methodical accuracy. To ensure the greatest of precision he constructed a vacuum chamber to hold his balance and noticed the erratic behaviour of his balance when in this vacuum. 

This led to his researches on “Repulsion resulting from Radiation” and the invention of his radiometer- a system of vanes, blackened on one side and polished on the other which rotated when exposed to radiant energy. From his findings, two main lines of research occupied Crookes: the properties of highly rarefied gases and the investigation of the elements of the “rare earths”.   

Crookes’ discoveries on the electrical discharge through rarefied gases found that a larger decrease in the gas led to a larger dark space around the negative electrode. By examining the properties of the rays, Crookes could demonstrate that they travelled in straight lines, caused phosphorescence in objects upon which they entered and thus produced heat.

His observations in the elements of the rare earths led to special methods having to be created in order to separate them as they were so similar to one another in their chemical properties. He concluded that ‘meta-elements’ existed that were clusters of elements that resembled each other so closely that they behaved as an individual.

The quartz spectrograph

His investigations in radiant matter spectroscopy were at first connected with the visible spectrum. He hoped that photography might be employed to record the spectra and that invisible bands in the ultra-violet region might be revealed. For this purpose, the quartz spectrograph was constructed and the first results were the discovery that the irregular phosphorescent spectrum extended further into the ultra-violet than had previously been observed.

With all of Crookes’ experimental work and painstaking research, he paved the foundation for later discoveries that changed the whole conception of chemistry and physics. His bibliography includes many published papers on spectroscopy, technical books on subjects ranging from chemistry, metallurgy, agriculture, and diamonds. 

His interests were wide and varied from electric lighting, the electric telegraph to the extraction of sugar from beetroot. He was concerned with applying scientific ideas to everyday life and warned his audience at an address to the British Association in 1898 that the world’s population would starve if new forms of nitrogenous fertilizers were not found. He served the government in an advisory capacity and applied his findings to improve many public services.


As Spiritualism grew in popularity during the nineteenth century, William Crookes, by now a scientist of international repute, decided to investigate it using scientific methods of recording. Originally Crookes had been sceptical about the phenomenon believing it to be mere trickery. However, after studying one of the most famous mediums, Daniel Dunglas Homes, he was convinced he was in possession of a powerful psychic force. 

It was his observations of the young Florence Cook that brought Crookes’ work to critical attention. Through Cook’s mediumship, Crookes witnessed the materialisation of the spirit Katie King, which Crookes was able to photograph several times. The scientific community met Crookes’ findings with hostility but he was convinced that there were forces at work outside the knowledge of mere mortals.

Despite his controversial work in Spiritualism Crookes was nonetheless an exceptional experimentalist, a laborious researcher and meticulous observer. In recognition of his work, he was knighted in 1897 and received the Order of Merit in 1910.  He received many honours including the Royal, Davy and Copley medals of the Royal Society and was their president between the years 1913-15. 

He was also president of the Chemical Society, the Society of Chemical Industry and the British Association. He was elected a Member of the Institution of Electrical Engineers (now the IET) in 1881 and became president in 1891.

He died in London on 4 April 1919.