A Positive Ray Spectrograph in The London, Edinburgh and Dublin Philosophical Magazine and Journal of Science, Vol. XXXVIII. Sixth Series. July-December 1919, pp. 707-714

London: Taylor & Francis, 1919. 1st Edition. HANDSOMELY BOUND FIRST EDITION OF FRANCIS ASTON'S INVENTION OF THE MASS SPECTOGRAPH, AN INSTRUMENT USED OBTAIN & RECORD THE SPECTRAL CONTENT OF LIGHT. Aston was awarded the 1922 Nobel Prize in Chemistry ""for his discovery, by means if his mass spectrograph, of isotopes, in a large number of non-radioactive elements, and for his enunciation of the whole-number rule" (Nobel Committee). Aston's invention separated and measured wavelengths in electromagnetic radiation, measuring the relative amounts of radiation at each wavelength.

Francis William Aston was an English physicist and chemist. Working at the Cavendish Laboratory, he began to confront the problem of the separation of the isotopes of neon. Thomson had earlier invented a parabola apparatus, but Aston wanted his invention to produce intense, clear photographs, meaning that he would need to focus a range of speeds at one point. To achieve this, Aston used a different arrangement of electric and magnetic fields. In Thomson's experiment, charged particles passed through both fields at the same time - meaning the fields were acting in the same position. Aston modified things, allowing his particles to be deflected by the field of electricity prior to entering the magnetic field.

Aston made other modifications, including the direction of the field. In Thomson's experiment, the fields moved both left and right as well as up and down. Aston rotated his electric field by ninety degrees; in this way, he insured that the ions would only move up and down. In Aston's experiment, slower particles passed through an electric or magnetic field and were then deflected by a greater amount than fast particles. "Aston positioned his two fields so that all the particles would be focussed onto the same spot, whatever their velocity. Aston had made an electromagnetic lens which focussed charged particles, similar to the way that an optical lens will focus light.

"The beam of charged particles is focussed with magnetic and electric fields. The position of the focussed spot depends only on the mass of the ions, not their velocity (or kinetic energy). These spots all lie on a straight line, and Aston put photographic paper along this line to record the masses. All the ions of the same mass hit the same point on the photographic strip, producing a dark spot. The position of these spots told Aston the masses of all the different ions within a beam.

"With his mass spectrograph, Aston quickly separated the two isotopes of neon and showed that Thomson's theory was correct. He also found that another common element, chlorine, showed two isotopes. The most important observation made with the first mass spectrograph was that the masses of the particles were always whole numbers, with the exception of hydrogen, whose mass was 1.008 on this scale. Many scientists thought that this 'whole number rule' meant that an atom's nucleus contained that number of protons, and enough electrons to account for the charge. We now know that this could not be the case, and such a nucleus would disintegrate very quickly. The problem was solved in 1932 when James Chadwick discovered the neutron. The neutron is an uncharged particle of almost the same mass as the proton, and the whole number rule can be satisfied if the nucleus contains only protons and neutrons" (Cambridge Physics Portal). CONDITION & DETAILS: London: Taylor & Francis. (8.5 x 5.5 inches). Complete. [viii], 752, [4]. 9 plates (including Aston plate); in-text illustrations throughout. Also included within is the original rear wrap of one issue. Ex-libris bearing a discreet perforated stamp on the title page. Solidly and tightly rebound in three quarter brown calf over marbled paper boards. Four gilt-ruled raised bands at the spine; gilt-lettered black morocco labels. The title page is slightly soiled and creased. Apart from this, volume is bright and clean throughout. Very good +.