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Crookes, Sir William

Category: Scientist


Sir William Crookes, OM, FRS (17 June 1832 – 4 April 1919) was a British chemist, physicist, meteorologist and lecturer in chemistry at the Chester Diocesan Training College. 
After having inherited a large fortune from his father, he devoted himself from 1856 entirely to scientific work of various kinds at his private laboratory in London.

Crookes wrote a standard treatise on Select Methods in Chemical Analysis in 1871; and in 1859, he founded the Chemical News, a science magazine aimed at promoting wider understanding of these discoveries; he both contributed to and edited the magazine for many years. 

Crookes’ cathode-ray studies were fundamental in the development of atomic physics and he was well known for the ingenuity of his experiments  “notable for the originality of their design and skill of execution”.  It recognised today that Crookes's experimental work was the foundation of discoveries which eventually changed the whole of chemistry and physics.

Crookes's house and laboratory

William Crookes (later Sir William Crookes) was born in London, the eldest of 16 siblings. His father, Joseph Crookes, was a tailor of north-country origin, at that time living with his second wife, Mary Scott Lewis Rutherford Johnson.  In 1856 William Crookes married Ellen, daughter of William Humphrey of Darlington. They had three sons and a daughter, he was a devoted family man.

He was elected a fellow of the Royal Society in 1863 and was knighted in 1897.  In 1910, Crookes received the Order of Merit.  He was also awarded the Royal Medal (1875), Davy Medal (1888), Albert Medal (1899), Copley Medal (1904) and Elliott Cresson Medal (1912).

After 1880, he lived at 7 Kensington Park Gardens where all his later work was done, in his private laboratory.  He died in London on 4 April 1919, two years after his wife. He is buried in London's Brompton Cemetery.

Discoveries and inventions



After studying at the Royal College of Chemistry, London, Crookes became superintendent of the meteorological department at Radcliffe Observatory, Oxford, in 1854, and the following year gained a post at the College of Science in Chester, Cheshire. At the Radcliffe Observatory in Oxford in 1854, he adapted the recent innovation of wax paper photography to continuously record meteorological data.

Chemical elements

Crookes is noted for his discovery of the element thallium.  With the introduction of spectrum analysis by R.W. Bunsen and G.R. Kirchhoff, Crookes applied the new technique to the study of selenium compounds. In 1861 he discovered thallium in some seleniferous deposits. He continued work on that new element, isolated it, studied its properties, and in 1873 determined its atomic weight.  Crookes also identified the first known sample of helium, in 1895.

Cathode rays and the Crookes tube


Crookes’ researches on electrical discharges through a rarefied gas led him to observe the dark space around the cathode, now called the Crookes dark space. He demonstrated that cathode rays travel in straight lines and produce phosphorescence and heat when they strike certain materials.

In his investigations of cathode ray display devices, he was one of the first scientists to identify what is now called a plasma and identified it as the fourth state of matter in 1879. If you prefer he was the first to discover so called ‘dark matter’.

A Crookes tube is an early experimental electrical discharge tube with vacuum, invented around 1869-1875, in which cathode rays, - streams of electrons,  - were discovered.

Developed from the earlier Geissler tube, the Crookes tube consists of a partially evacuated glass bulb of various shapes, with two metal electrodes, the cathode and the anode, one at either end. When a high voltage is applied between the electrodes, cathode rays (electrons) are projected in straight lines from the cathode. It was used by Crookes, Johann Hittorf, Julius Plücker, Eugen Goldstein, Heinrich Hertz, Philipp Lenard and others to discover the properties of cathode rays, culminating in J.J. Thomson's 1897 identification of cathode rays as negatively charged particles, which were later named electrons.  Wilhelm Röntgen discovered X-rays using the Crookes tube in 1895.


The Crookes radiometer


During his studies of thallium, around about 1873, Crookes discovered the principle of the Crookes radiometer, a device that converts light radiation into rotary motion. In the course of very accurate quantitative chemical work, he was weighing samples in a partially evacuated chamber to reduce the effect of air currents, and noticed the weighings were disturbed when sunlight shone on the balance. Investigating this effect, he created the device named after him.

The principle of this radiometer has found numerous applications in the development of sensitive measuring instruments.  Also known as a light mill, it consists of an airtight glass bulb, containing a partial vacuum. Inside are a set of vanes which are mounted on a spindle. The vanes rotate when exposed to light, with faster rotation for more intense light, providing a quantitative measurement of electromagnetic radiation intensity.


In 1903, Crookes turned his attention to the newly discovered phenomenon of radioactivity, achieving the separation from uranium of its active transformation product, uranium-X (later established to be protactinium). Crookes 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 "p-particles", ejected from radio-active substances, impinge upon zinc sulfide, 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 radioactivity.

He also devised one of the first instruments for the studying nuclear radioactivity, the spinthariscope.


Crookes became interested in spiritualism in the late 1860s. His interest lay principally in whether one could apply experimental procedures to spiritual events. 

The difficulty of very many spiritual experiences is that the people to whom they occur are not in control of them.  Daniel Dunglas Hume, for example, was frequently in a trance condition and totally unaware when he came out of the trance of what had happened.  Home and a great number of other mediums of the time stated categorically that they were in a sense ‘possessed’.  By what they were possessed was a subject of debate, but it was accepted that experiments could not be repeated, and Crookes decided that he would use his considerable ingenuity to devise experiments that could at least measure some of the phenomenon occurring.  


Some weeks ago the fact that I was engaged in investigating Spiritualism, so called, was announced in a contemporary magazine and in consequence of the many communications I have since received, I think it desirable to say a little concerning the investigation which I have commenced.


Views or opinions I cannot be said to possess on a subject which I do not pretend to understand. I consider it the duty of scientific men who have learnt exact modes of working, to examine phenomena which attract the attention of the public, in order to confirm their genuineness, or to explain, if possible, the delusions of the honest and to expose the tricks of deceivers. But I think it a pity that any public announcement of a man's investigation should be made until he has shown himself willing to speak out.  A man may be a true scientific man, and yet agree with Professor De Morgan, when he says-

" I have both seen and heard, in a manner which would make unbelief impossible, things called spiritual, which cannot be taken by a rational being to be capable of explanation by imposture, coincidence, or mistake. So far I feel the ground firm under me; but when it comes to what is the cause of these phenomena, I find I cannot adopt any explanation which has yet been suggested. . . . The physical explanations which I have seen are easy, but miserably insufficient.  The spiritual hypothesis is sufficient, but ponderously difficult."

Regarding the sufficiency of the explanation, I am not able to speak. That certain physical phenomena, such as the movement of material substances, and the production of sounds resembling electric discharges, occur under circumstances in which they cannot be explained by any physical law at present known, is a fact of which I am as certain as I am of the most elementary fact in chemistry.


My whole scientific education has been one long lesson in exactness of observation, and I wish it to be distinctly understood that this firm conviction is the result of most careful investigation. But I cannot, at present hazard even the most vague hypothesis as to the cause of the phenomena…..

Faraday says, "Before we proceed to consider any question involving physical principles, we should set out with clear ideas of the naturally possible and impossible".

But this appears like reasoning in a circle: we are to investigate nothing till we know it to be possible, whilst we cannot say what is impossible, outside pure mathematics, till we know everything.

In the present case I prefer to enter upon the enquiry with no preconceived notions whatever as to what can or cannot be,  but with all my senses alert and ready to convey information to the brain; believing, as I do that we have by no means exhausted all human knowledge or fathomed the depths of all the physical forces, and remembering that the great philosopher already quoted said, in reference to some speculations on the gravitating force " Nothing is too wonderful to be true, if it be consistent with the laws of nature; and in such things as these, experiment is the best test of such consistency."

The modes of reasoning of scientific men appear to be generally misunderstood by spiritualists with whom I have conversed, and the reluctance of the trained scientific mind to investigate this subject is frequently ascribed to unworthy motives. I think, therefore it will be of service if I here illustrate the modes of thought current amongst those who investigate science, and say what kind of experimental proof science has a right to demand before admitting a new department of knowledge into her ranks.

We must not mix up the exact and the inexact. The supremacy of accuracy must be absolute.


The first requisite is to be sure of facts; then to ascertain conditions; next laws. Accuracy and knowledge of detail stand foremost amongst the great aims of modern scientific-men. No observations are of much use to the student of science unless they are truthful and made under test conditions; and here I find the great men of spiritualistic evidence to fail.

In a subject which, perhaps, more than any other lends itself to trickery and deception, the precautions against fraud appear to have been, in most cases, totally insufficient owing, it would seem, to an erroneous idea that to ask for such safeguards was to imply a suspicion of the honesty of someone present. We may use our own unaided senses, but when we ask for instrumental means to increase their sharpness, certainty, and trustworthiness under circumstances of excitement and difficulty and when one's natural senses are liable to be thrown off their balance, offence is taken.

In the countless number of recorded observations I have read, there appear to be few instances of meetings held for the express purpose of getting the phenomena under test conditions, in the presence of persons properly qualified by scientific training to weigh and adjust the value of the evidence which might present itself. The only good series of test experiments I have met with were tried by the Count de Gasparin, and he, whilst admitting the genuineness of the phenomena, came to the conclusion that they were not due to supernatural agency……..


In investigations which so completely baffle the ordinary observer, the thorough scientific man has a great advantage.

He has followed science from the beginning through a long line of learning, and he knows, therefore in what direction it is leading; he knows that there are dangers on one side, uncertainties on another, and almost absolute certainty on a third: he sees to a certain extent in advance. But, where every step is towards the marvellous and unexpected, precautions and tests should be multiplied rather than diminished. Investigators must work; although their work may be very small in quantity if only compensation be made by its intrinsic excellence. But, even in this realm of marvels,-this wonderland towards which scientific enquiry is sending out its pioneers - can anything be more astonishing than the delicacy of the instrumental aids which the workers bring with them to supplement the observations of their natural senses?


The spiritualist tells of bodies weighing 50 or 100 lbs. being lifted up into the air without the intervention of any known force; but the scientific chemist is accustomed to use a balance which will render sensible a weight so small that it would take ten thousand of them to weigh one grain; he is, therefore justified in asking that a power, professing to be guided by intelligence, which will toss a heavy body up to the ceiling, shall also cause his delicately-poised balance to move under test conditions.

The spiritualist tells of tapping sounds which are produced in different parts of a room when two or more persons sit quietly round a table. The scientific experimenter is entitled to ask that these taps shall be produced on the stretched membrane of his phonautograph.

The spiritualist tells of rooms and houses being shaken, even to injury, by superhuman power. The man of science merely asks for a pendulum to be set vibrating when it is in a glass case and supported on solid masonry.


The spiritualist tells of heavy articles of furniture moving from one room to another without human agency. But the man of science has made instruments which will divide an inch into a million parts; and he is justified in doubting the accuracy of the former observations, if the same force is powerless to move the index of his instrument one poor degree.

The spiritualist tells of flowers with the fresh dew on them, of fruit, and living objects being carried through closed windows, and even solid brick-walls. The scientific investigator naturally asks that an additional weight (if it be only the 1000th part of a grain) be deposited on one pan of his balance when the case is locked. And the chemist asks for the 1000th of a grain of arsenic to be carried through the sides of a glass tube in which pure water is hermetically sealed.

The spiritualist tells of manifestations of power, which would be equivalent to many thousands of "foot-pounds" taking place without known agency. The man of science believing firmly in the conservation of force and-that it is never produced without a corresponding exhaustion of something to replace it asks for some such exhibitions of power to be manifested in his laboratory, where he can weigh, measure and submit it to proper tests.


For these reasons and with these feelings I began an inquiry suggested to me by eminent men exercising great influence on the thought of the country. At first, like other men who thought little of the matter and saw little, I believed that the whole affair was a superstition, or at least an unexplained trick, Even at this moment I meet with cases which I cannot prove to be anything else; and in some cases I am sure that it is a delusion of the senses.

I by no means promise to enter fully into this subject; it seems very difficult to obtain opportunities, and numerous failures certainly may dishearten anyone. The persons in whose presence these phenomena take place are few in number, and opportunities for experimenting with previously arranged apparatus are rarer still. I should feel it to be a great satisfaction if I could bring out light in any direction, and I may safely say that I care not in what direction.

….At present the phenomena I have observed baffle explanation; so do the phenomena of thought, which are also spiritual, and which no philosopher has yet understood. No man, however, denies them.

In justice to my subject, I must state that, on repeating these views to some of the leading ‘spiritualists’ and most trustworthy ‘mediums’ in England, they express perfect confidence in the success of the enquiry, if honestly carried out in the spirit here exemplified ; and they have offered to assist me to the utmost of their ability, by placing their peculiar powers at my disposal. As far as I have proceeded, I may as well add that the preliminary tests have been satisfactory.


Crookes joined the Society for Psychical Research, becoming its president in the 1890s, in order to put his work into a wider fled of scientific discussion and also enable him to draw on witnesses and assistance from the SPR when he needed them.

Crookes studied the mediums Kate Fox, Florence Cook, and Daniel Dunglas Home. But found Daniel Dunglas Home to be the most consistent and interesting subject. 

We have the results of his experiments with Home under Home himself, but have also included his paper on the results from his more general studies.


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