Joseph John ThoMSon (1856-1940)

The father of mass spectrometry, J. J. Thomson was an English physicist at Cambridge University. By using the first “mass spectrometer” he discovered the electron, measured its m/z, and was the first to succeed in differing positive particles according to their m/z values.

Figure 1. J. J. Thomson, the father of mass spectrometry.


The discovery of the electron

Thomson discovered the electron during his experiments designed to study the nature of cathode rays.  When a high voltage was applied across partially evacuated glass tubes, some kind of ray that was emitted by the cathode produced a fluorescent glow when reached the glass. These rays were called cathode rays (Figure 2) and the controversy on their ondulatory or corpuscular nature lasted for 25 years. Finally in 1897, J. J. Thomson proved that cathode rays acted like charged particles by showing that a narrow luminous beam produced by using an aperture near the cathode could be deflected by either an electric field or a magnetic field (Figure 3).

Figure 2. Cathode ray tube.  See also:

Figure 3. J. J. Thomson Parabola Mass Spectrometer.

Thomson found that the charge-to-mass ratio (m/z) and the velocity of a particle could be measured by balancing the deflections with the application of both electric and magnetic fields. This same principle is presently used in velocity selectors for mass spectrometers.

Thomson measured the m/z for different gas fillings of the tube but found that the value was always the same. Thus, he concluded that the negatively charged particles were contained in all atoms. From the perception of solid matter, he presumed that the positive residual matter filled the entire space of the atom, giving rise to what has been called the “Thomson model” of the atom (Figure 4).

Figure 4. Thomson’s plum pudding atomic model. In this model, the atom is composed of "corpuscles" (electrons) surrounded by a soup of positive charge to balance the electron's negative charge, like negatively-charged "plums" surrounded by cloud of positive charge ("pudding"). The electrons were thought to be positioned throughout the atom, but with many structures possible for positioning multiple electrons, particularly rotating rings of electrons.


J. J. Thomson received the Nobel Prize in physics in 1906 … "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases"


The First Mass Spectra

After having elucidated the nature of cathode rays and discovered the electron,  J. J. Thomson turned his attention to the study of positive rays. Positive rays called canal rays and they streamed through the holes into the space behind the cathode travelling in the opposite direction from cathode rays (Figure 5).

Figure 5. Cathode rays and canal rays.

J. J. Thomson investigated these rays, which behaved very differently from cathode rays, operating his cathode ray tube at lower pressures and using parallel fields, magnetic and electrostatic, to give crossed deflexions. The rays were received on a photographic plate and co-ordinates measured on this gave the magnetic and electrostatic deflexions respectively (Figure 6).


Figure 6. Positive ray parabolas. The first “ mass spectra”.


First with hydrogen, and later with other atoms and molecules of carbon, nitrogen and oxygen, Thomson discovered that each charged particle followed its own parabolic path based upon their detection on the photographic plate. He reasoned that no two particles would follow the same path unless they possessed the same charge-to-mass ratio. Thomson quickly realized that an inspection of the plate shows at a glance how many kinds of particles there were in the rays.

In his recollections, published in 1936, four years before his death, Thomson recounted that the positive rays contained atoms and molecules of all gases, common elements or molecules present, and correctly suggested that the positively charged particles were formed by the loss of an electron.

Thomson concluded that the positive ray spectra possessed many advantages over other approaches for chemical analysis. The number of components as well as their atomic or molecular weight could be measured from these spectra. Another noted advantage was that the method was not dependent on the purity of gas analysed. Impurities merely appeared as additional parabolas in the spectrum and did not contribute erros to measurements of atomic or molecular weight. Thus the field of mass spectrometry was born and these important features, recognized by Thomson, remain to this day.


Two Famous quotes by J. J. Thomson

1. J.J. Thomson's inaugural presidential address to the British Association as published in Nature (1909). Sir Joseph concludes his address with these historical words:

"As we conquer peak after peak we see in front of us regions full of interest and beauty, but we do not see our goal, we do not see the horizon; in the distance tower still higher peaks, which will yield to those who ascend them still wider prospects, and deepen the feeling, the truth of which is emphasized by every advance in science, that 'Great are the Works of the Lord'."
(Thomson 1909, Nature, vol. 81, p. 257).

2. J. J. Thomson, speaking on mass spectrometry in 1903, put forward this prophetic statement about the features of mass spectrometry (Speed, Sensitivity, Selectivity, Universality, Characterization of Transient Reaction Intermediates, Chemical Reaction Monitoring):

 “I feel sure that there are many problems in chemistry which could be solved with far greater ease by this than any other method (Universal) . The method is surprisingly sensitive-more so even than that of Spectrum Analysis, requires an infinitesimal amount of material and does not require this to be specially purified: . . . the rays are registered on the photograph within much less than a millionth of a second after their formation, so that when chemical combination or decomposition is going on in the gas in the tube, the method may disclose the existence of intermediate forms which have only transient existence, as well as that of the final product, and may thus enable us to get a clearer insight into the processes of chemical combination."”

[a) Thomson, J. J. "Rays of Positive Electricity and Their Application to Chemical Analyses"; Longmans Green and Co: London, 1913: p 56. b) Thomson, J. J. "Recollections and Reflections"; Cambridge University Press: Cambridge, 1937].

J.J. Thomson
The Nobel Prize in Physics 1906


Joseph John Thomson was born in Cheetham Hill, a suburb of Manchester on December 18, 1856. He enrolled at Owens College, Manchester, in 1870, and in 1876 entered Trinity College, Cambridge as a minor scholar. He became a Fellow of Trinity College in 1880, when he was Second Wrangler and Second Smith's Prizeman, and he remained a member of the College for the rest of his life, becoming Lecturer in 1883 and Master in 1918. He was Cavendish Professor of Experimental Physics at Cambridge, where he succeeded Lord Rayleigh, from 1884 to 1918 and Honorary Professor of Physics, Cambridge and Royal Institution, London.

Thomson's early interest in atomic structure was reflected in his Treatise on the Motion of Vortex Rings which won him the Adams Prize in 1884. His Application of Dynamics to Physics and Chemistry appeared in 1886, and in 1892 he had his Notes on Recent Researches in Electricity and Magnetism published. This latter work covered results obtained subsequent to the appearance of James Clerk Maxwell's famous "Treatise" and it is often referred to as "the third volume of Maxwell". Thomson co-operated with Professor J. H. Poynting in a four-volume textbook of physics, Properties of Matter and in 1895 he produced Elements of the Mathematical Theory of Electricity and Magnetism, the 5th edition of which appeared in 1921.

In 1896, Thomson visited America to give a course of four lectures, which summarised his current researches, at Princeton. These lectures were subsequently published as Discharge of Electricity through Gases (1897). On his return from America, he achieved the most brilliant work of his life - an original study of cathode rays culminating in the discovery of the electron, which was announced during the course of his evening lecture to the Royal Institution on Friday, April 30, 1897. His book, Conduction of Electricity through Gases, published in 1903 was described by Lord Rayleigh as a review of "Thomson's great days at the Cavendish Laboratory". A later edition, written in collaboration with his son, George, appeared in two volumes (1928 and 1933).

Thomson returned to America in 1904 to deliver six lectures on electricity and matter at Yale University. They contained some important suggestions as to the structure of the atom. He discovered a method for separating different kinds of atoms and molecules by the use of positive rays, an idea developed by Aston, Dempster and others towards the discovery of many isotopes. In addition to those just mentioned, he wrote the books, The Structure of Light (1907), The Corpuscular Theory of Matter (1907), Rays of Positive Electricity (1913), The Electron in Chemistry (1923) and his autobiography, Recollections and Reflections (1936), among many other publications.

Thomson, a recipient of the Order of Merit, was knighted in 1908. He was elected Fellow of the Royal Society in 1884 and was President during 1916-1920; he received the Royal and Hughes Medals in 1894 and 1902, and the Copley Medal in 1914. He was awarded the Hodgkins Medal (Smithsonian Institute, Washington) in 1902; the Franklin Medal and Scott Medal (Philadelphia), 1923; the Mascart Medal (Paris), 1927; the Dalton Medal (Manchester), 1931; and the Faraday Medal (Institute of Civil Engineers) in 1938. He was President of the British Association in 1909 (and of Section A in 1896 and 1931) and he held honorary doctorate degrees from the Universities of Oxford, Dublin, London, Victoria, Columbia, Cambridge, Durham, Birmingham, Göttingen, Leeds, Oslo, Sorbonne, Edinburgh, Reading, Princeton, Glasgow, Johns Hopkins, Aberdeen, Athens, Cracow and Philadelphia.

In 1890, he married Rose Elisabeth, daughter of Sir George E. Paget, K.C.B. They had one son, now Sir George Paget Thomson, Emeritus Professor of Physics at London University, who was awarded the Nobel Prize for Physics in 1937, and one daughter.

From Nobel Lectures, Physics 1901-1921, Elsevier Publishing Company, Amsterdam, 1967.

This autobiography/biography was written at the time of the award and first published in the book series Les Prix Nobel. It was later edited and republished in Nobel Lectures. To cite this document, always state the source as shown above.

For more updated biographical information, see: Thomson, Joseph John, Recollections and Reflections. G. Bell and Sons: London, 1936.

J.J. Thomson died on August 30, 1940.


George P. Thomson