In this installment on the history of atom theory, physics professor (and my dad) Dean Zollman discusses a couple of scientific dead ends – the ether and vortex atoms. – Kim
By Dean Zollman
The last half of the 19th century saw a variety of advances related to our understanding of atoms. We discussed a very important one last time – Balmer’s formula for the wavelength of the visible lines of hydrogen. This equation created a challenge that needed to be explained by any successful model of the atom. That challenge would not be met until the 20th century. In the meantime, scientists pursued research, some with advances and some with dead ends.
One mathematical model which indicated that matter was made up of small objects was the kinetic theory of gases. This theory is a way to understand how and why pressure, volume, and temperature are related in gasses that are trapped in a container. The gas is hypothesized to be a collection of small hard particles. In the simplest model, these particles are spheres. The small particles are moving in random motion with many different speeds. However, the temperature is related to the average speed of the collection of particles.
Many scientists such a Rudolf Clausius (1822 – 1888), James Clerk Maxwell (1831 – 1879), and Ludwig Boltzmann (1844 – 1906) contributed to the development of our understanding of the relations among measurable variables of gasses and some small particles in constant motion. To see simulations of these relationships, you can play with the computer visualization at PhET.
While kinetic theory provided strong evidence that gases probably consisted of small particles, it did not help scientists understand the structure of the particles themselves. This theory was developed mostly with the idea that the particles were too small to see and that they bounced off each other and the walls of their container.
The Ether and Vortex Atoms
Another theory developed about the same time did try to go deeper into the structure of the atom. To understand it, we need first to look at a “solution” to another mystery of that time. The mystery involved the propagation of light and forces acting at a distance. Light was shown to be a wave phenomenon early in the 19th century. However, waves, such as water waves, moved through a medium.
So the question was: how could light get to us from distance locations such as the sun? There seemed to be no medium through which these light waves could move. Likewise, forces such as electrical, magnetic, and gravitational forces acted at a distance. How could that action occur if there were no medium through which the force travelled? The solution was to propose a substance called the ether (or aether). This substance filled all of space and thus offered a medium for the various forces and light. However, because no one had ever detected it, the ether needed to be invisible and not measurable in any way.
Hermann von Helmholtz (1821 – 1894) was not thinking about the ether or atoms when he was conducting research on the dynamics of fluids. Instead, he was creating a mathematical model of vortices, the rotating motion that we see when we let water out of the sink. Helmholtz developed mathematically many properties of the core of the vortex and that vortices could apply forces to one another. (Photo to the right of a vortex in a bottle of water by Robert D Anderson, used under the terms of the GNU Free Documentation License, via Wikimedia Commons.)
Peter Tait (1831 – 1901) became interested in these ideas and developed an experiment for creating smoke rings which behaved as vortices. His apparatus is shown below.
Tait showed his smoke rings to William Thomson, who was later to become Lord Kelvin (1824 – 1907). He demonstrated that these smoke vortices were remarkably stable. That they could be cut with a knife but would reform and that they could collide with each other but held their shape. These experiments together with Helmholtz’s mathematics reminded Kelvin of the properties of atoms.
In 1867, Kelvin wrote to Helmholtz that if there is an ether, a vortex ring in that ether “would be as permanent as the solid hard atoms of Lucretius …” (quoted in Helge Kraugh, “The Vortex Atom: A Victorian Theory of Everything” Centaurus, 2002). With this thought, Kelvin and others started developing a theory of atoms as vortices in the ether.
Scientists Drawn into the Vortex (Atoms)
Many people got involved in the studies of vortex atoms. I will mention only a few. William Mitchinson Hicks (1850 – 1934) showed that a hollow vortex atom would vibrate. These vibrations would presumably lead to the emission of light and thus explain the spectrum emitted by the different atoms. However, I cannot find evidence that he was able to match data with the vibrations.
In fact, Lord Kelvin found the mathematics of the vibrations quite difficult so he relied on analogies with smoke rings. He stated, “it is probable that the vibrations which constitute the incandescence of sodium vapour are analogous to those which the smoke rings had exhibited.” He also addressed the issue that sodium has two yellow spectral lines which are very close together in wavelength. “Since, however, sodium light shows two sets of vibrations with slightly different periods and about equal intensity, the sodium atom must have two fundamental modes of vibration, and therefore it seems probable that the sodium atom may not consist of a single vortex line, but of two approximately equal vortex rings passing through one another like two links in a chain.” (Quoted in Robert Silliman, William Thomson: “Smoke Rings and 19th Century Atomism”, Isis 54, 461-474 (1963).)
Alfred Marshall Mayer (1836 – 1897) looked at the chemistry related to configurations of vortex atoms. The mathematics was very complex, so he did it experimentally. He simulated each vortex with a magnetized needle. Then he floated the needles on water with a larger magnet held above them. For 2 to 20 magnetized needles, he looked at the stable configuration created by the attractive and repulsive forces of the small magnets in the presence of the larger magnet. When he looked at the results (see below), he saw some periodic behavior in the patterns (We will return to this experiment when we look at another model of the atom in a few months.)
Joseph J. Thomson (1856 – 1940) was a rather young physicist when he became involved in vortex atoms. He seems to be the first to notice a connection between Mayer’s floating magnets and the periodic table. He attempted to use the vortex model to explain some chemical properties. In 1883, he published an essay “Vortex Atom Rings.” Most importantly, his studies on vortex atoms caused him to become interested in electricity and electrical discharges in gases. The research related to these interests led to one of the most important discoveries in the development of our understanding of the structure of the atom. We will save that story for next time.
Interesting Results But…
Research on the vortex atom provided many interesting results. However, as the 19th century was winding down, the vortex atom was falling out of favor with scientists.
About 1883, Kelvin started expressing concerns. He worried that the vortex atom could not explain inertia or gravitational attraction. (Perhaps he should not have worried about gravity; it is still somewhat perplexing.) Eventually he concluded that Helmholtz’s rings were not as stable as he had originally thought.
By 1898, he wrote to an emeritus professor at MIT: “I am afraid it is not possible to explain all the properties of matter by the Vortex-atom Theory alone … We may expect that the time will come when we shall understand the nature of an atom. With great regret I abandon the idea that a mere configuration of motion suffices.” (Quoted in Silliman). In the early 20th century, both experiment and theory concluded that the ether did not exist. However, the development of the theory contributed to several mathematical advances (e.g., theory of knots).
Vortex atoms kept a lot of scientists, particularly in the U.K. and U.S., busy for quite a while. In the long run it proved to be a dead end in terms of explaining the structure of matter. However, the development of the theory led to many useful mathematical results, some of which are being revived for other purposes today. It also provided a beginning for J.J. Thomson. Thus, while the theory did not meet the goals of its originator, it did help advance science and thoughts about the structure of matter.
Dean Zollman is university distinguished professor of physics at Kansas State University where he has been a faculty member for more than 40 years. During his career he has received four major awards — the American Association of Physics Teachers’ Oersted Medal (2014), the National Science Foundation Director’s Award for Distinguished Teacher Scholars (2004), the Carnegie Foundation for the Advancement of Teaching Doctoral University Professor of the Year (1996), and AAPT’s Robert A. Millikan Medal (1995). His present research concentrates on the teaching and learning of physics and on science teacher preparation.