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. 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.
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. His bibliography includes many published papers on spectroscopy, technical books on subjects ranging from chemistry, metallurgy, agriculture, and diamonds. Crookes's life was one of unbroken scientific activity.
He was never one of those who gain influence by popular exposition. The breadth of his interests, ranging over pure and applied science, economic and practical problems, and psychical research, made him a well-known personality, and he received many public and academic honours.
In he founded the Chemical News a science magazine, which he edited for many years and conducted on much less formal lines than is usual with journals of scientific societies. Crookes was knighted in , and in received the order of merit. He died in London on 4 April , two years after his wife, to whom he had been much devoted.
Crookes is buried in London's Brompton Cemetery. The work of Crookes extended over both chemistry and physics. Its salient characteristic was the originality of conception of his experiments, and the skill of their execution.
Crookes was always more effective in experiment than in interpretation. The method of spectral analysis, introduced by Bunsen and Kirchhoff , was received by Crookes with great enthusiasm and to great effect. His first important discovery was that of the element thallium , announced in , and made with the help of spectroscopy.
By this work his reputation became firmly established, and he was elected a fellow of the Royal Society in Crookes' attention had been attracted to the vacuum balance in the course of the thallium researches. He soon discovered the phenomenon upon which depends the action of the well-known little instrument, the Crookes radiometer , in which a system of vanes, each blackened on one side and polished on the other, is set in rotation when exposed to radiant energy.
Crookes did not, however, provide the true explanation of this apparent "attraction and repulsion resulting from radiation ". Crookes published numerous papers on spectroscopy , a subject which always had a great fascination for him, and he conducted research on a large variety of minor subjects. In addition to various technical books, he wrote a standard treatise on Select Methods in Chemical Analysis in , and a small book on Diamonds in Crookes investigated the properties of cathode rays, showing that they travel in straight lines, cause phosphorescence in objects upon which they impinge, and by their impact produce great heat.
The material was left over from earlier work on sulpho-selenides in which he had engaged at the College of Science. Crookes was a good experimenter, and he followed up his initial observation by isolating the new element and investigating its properties. A sample was inevitably shown at the Great Exhibition of and recognition very quickly followed too quickly, some declared by his election as a fellow of the Royal Society in November President of the Royal Society from to , Sir William Crookes died fifty years ago this month at the age of Most of his working life spanned an era in which a man could take very nearly the whole of science as his province.
It was thus almost inevitable that the platinum metals should have been included among his many interests, and his observations on the loss of weight of the platinum group metals when heated in air have indeed been quoted as authoritative for nearly half a century.
In this detail from a painting by II. The occasion was the demonstration by Dewar in of the properties of liquid hydrogen. His determination of the atomic weight of thallium, reported in , was a first-class piece of work and the figure he obtained, His flair for careful observation continued to serve him well. He devised the radiometer — though his explanation of its action was soon discredited — he described the Crookes dark space in the cathode discharge tube — but was less than profound in his theoretical views on electrical discharges through gases — he separated Uranium X, he devised the spintharoscope, and he developed Crookes glass to protect the eye against the ultra-violet.
In his later years, like Sir Oliver Lodge, he explored the mysteries of spiritualism. In another tube, Crookes included a paddle wheel that turned when bombarded with cathode rays, and he used a Y-shaped tube to show that cathode rays would travel towards an anode even if it was not located directly in front of the cathode.
Crookes further demonstrated that cathode rays can be bent by a magnetic field and carefully investigated the changing colors and effects in the tubes as they became increasingly evacuated. He was the first to note the dark space now termed the Crookes dark space that appears near the cathode at very low pressure, and correctly speculated that the space was a region in which the cathode rays moved freely before colliding with the gas molecules present in the tube, which he believed was responsible for producing the characteristic glow.
When J. Crookes was a very open-minded scientist, however, and despite his advanced years at the time, he willingly acknowledged the ascendancy of better interpretations of his experimental work than he had been able to develop at the time. In particular, he was fascinated by psychic phenomena and undertook the study of several famous spiritual mediums.
For his work in this area, Crookes was often ridiculed, but throughout his life he steadfastly maintained the reality of the psychic phenomena he witnessed. A less controversial interest of Crookes was journalism. He was founder of the Chemical News , which he edited from its inception in until Other notable achievements include the invention of the spinthariscope , the study of radioactive materials, the design of protective eyewear for use by glassblowers and the publication of texts on chemical analysis and diamonds.
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