• Choose a category
• All
• Classic-Fiction

By Root 1058 0

century interest in the phenomenon of electricity had generated research into the behaviour of the force in gases. In 1855 Johann Geissler had shown that a current passed through a rarefied gas held in a glass tube caused the tube to glow. In 1859 Julius Plücker used magnets to make the glow move, and observed that the glow appeared to come from the walls of the tube itself. In 1869 his pupil Johann Hittorf looked closer. In a high vacuum he saw that the glow came from the negative pole, or the cathode, and moved in a straight line towards the positive pole, or anode. He established this because an object placed in the way of the rays cast a shadow.

The cathode rays attracted immense attention towards the end of the century. Philipp Lenard, Hertz’s pupil, found that the rays would go through gold or aluminium foil which was otherwise totally opaque to light. In 1896 J. J. Thomson at Cambridge noticed that if a window was opened in the cathode tube the rays would escape, but only travel a few centimetres in the air before losing their ability to glow. He concluded this must be due to the fact that the rays were actually formed of particles smaller than the atoms of air, which impeded their progress. If this were so, the particles were sub-atomic in size.

William Crookes’experiment with cathode rays. Inside a depressurised tube, an anode (b) is placed in the path of cathode rays (a). The perfect geometrical shadow (d) cast by the anode reveals that the rays travel in straight lines.

Thomson established the existence of the particles by the use of magnetic deflection which showed that they possessed mass - that they were indeed particles. The ‘electrons’were obviously basic units of electricity. The problem which now began to emerge was another which profoundly disturbed those who viewed the universe in a Newtonian way. The particles existed, but the ray was a form of light and this was supposed to be a wave. How could a wave be a particle?

In 1900 Max Planck announced in Berlin that during experiments to observe the way in which hot bodies gave off energy, he had discovered that the energy was not released as expected in a continuous manner, but in small units, or packets of energy. As the release of energy increased it did so in bursts which were larger and larger multiples of the original unit. He called this basic energy unit, which was constant in relation to the frequency of the energy wave, a quantum, or ‘amount’. Waves of energy appeared to consist of separate amounts.

This went some way to explaining another discovery by Thomson. During his experiments with particles, he shone ultraviolet light in a vacuum at certain metals and discovered that they gave off electrons. The problem was that although the light was diffused all over the plate, spreading whatever energy it had, the metal gave off the electrons immediately.

In another of his 1905 papers Einstein explained what was happening. The light was arriving in packets of energy units as described by Planck. These knocked electrons out of the metal, and as the frequency of the light rose, so too did the number of electrons released. This also explained the mysterious effect of ultraviolet on Hertz’s spark. The light packets were adding energy to the spark and lengthening it. By now it was increasingly obvious that the old theory of waves of energy was extremely questionable. Einstein was saying something which made no sense. The question remained: how could waves be particles?

J. J. Thomson, Nobel prize-winner who discovered the first sub-atomic particle.

In 1927 Louis de Broglie took the bull by the horns and carried out an experiment in which photons, or light packets, were sent, one at a time, through the double pinhole system which Young had used more than a century before to establish the wave motion of light through interference. The photons interfered with each other as if they were waves.

In the same year two Americans were examining the way electrons were scattered when fired at a nickel target in a vacuum. At one point their vacuum tube exploded.