Geoscience Reference
In-Depth Information
same phenomenon, and in 1865 proposed a unifying theory of electromagnetism through
his publication “A dynamical theory of the electromagnetic field.” In 1876, the German
physicist Eugen Goldstein coined the phrase
cathode rays
when he demonstrated that the
glow from the cathode cast a shadow (Hedenus,
2002
). The English scientist Sir William
Crookes developed the first cathode ray tube during the 1870s with high vacuums. Using
these tubes he was able to demonstrate that luminescence rays appearing within the tube
actually carried energy from the cathode to the anode. Crookes also deflected these cathode
rays using magnetism and showed that the cathode beam behaved as if it were negatively
charged. In 1879, he proposed that these observations could be explained by a fourth state
of matter in which negatively charged molecules were projected at high velocities from
the cathode. Crookes termed this proposed fourth state “radiant matter” (Crookes,
1879
;
Eliezer & Eliezer,
2001
).
Edmund Becquerel's work and the conversion of light into electricity were of great
interest to the German physicist Heinrich Hertz. In 1887, before the discovery of the elec-
tron, Hertz performed experiments demonstrating that an electric spark across an air gap
between two electrodes is more easily emitted when ultraviolet light is shone on the cathode.
Finally, in 1897, in his experiments investigating how gases at low temperatures conducted
electricity, J. J. Thomson proved that cathode rays were composed of negatively charged
particles
that we now know as electrons, and that these particles were much lighter than the
smallest ions known at that time, hydrogen. These observations (Thomson,
1897a
,
b
), along
with the accidental discovery of radioactivity from studies performed on natural fluoresc-
ing minerals by Antoine Henri Becquerel (
1896
) at the same time, provided evidence that
atoms are not indestructible and that they are composed of
subatomic
particles. Thomson
realized that because many atoms appeared to be electrically, other “positively charged”
subatomic particles must also exist within the atom. It was in 1903 that Thomson postu-
lated that individual atoms were spheres of “uniform positive electrification,” scattered
with electrons rather like “currants” in a bun.
1.2.1.2 Quantized Matter and Energy
Before the discovery of the electron and the possibility of further subatomic particles,
matter was known to have mass, chemical and electromagnetic properties. In the main, the
aspects of matter that gave rise to many of the observed chemical and electrical properties
were still largely unknown during the late 19th century. It was generally accepted that the
arrangement of matter involved the presence of tiny oscillating particles (invisible to the
naked eye) and that it was these oscillating properties that gave rise to observed chem-
ical and physical properties. In 1894 Wilhelm Wien used theories about heat, and also
Maxwell's electromagnetic theories, to account for the relationship between wavelength
distribution and radiated heat energy from a theoretical body of matter that absorbed
all
radiation (black-body). In 1896 Wilhelm Wien performed experiments designed to under-
stand the spectral radiance of electromagnetic radiation from a black body in thermody-
namic equilibrium (within a cavity). Wien presented his laws of thermal radiation work
in a Nobel lecture given in December 1911 (Wien,
1911
). Wien's Law accurately predicts
