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Time for another post about the history of atom theory from award-winning physics professor (and my dad) Dean Zollman. Today, we meet 18th century scientists who were unsatisfied with the idea that forces acted on particles and came up with alternatives to explain their observations. – Kim

By Dean Zollman

Dean ZollmanAs we have discussed in the previous two posts, Sir Isaac Newton (1642-1727) had many ideas correct in his model of matter. Perhaps most importantly, he concluded that the particles of matter which were too small to see interacted via forces. Further, these forces decreased in strength as the particles moved further away from each other.

Today’s models of matter have several types of particles and four different forces. However, Sir Isaac’s model was pointing in the right direction. Yet, as we shall see, the idea of small particles interacting via forces lost favor with researchers, particularly in the 18th and 19th centuries. In this post, we will look at some of the reasons.

Portrait of Sir Isaac Newton, Godfrey Kneller, 1702

Portrait of Sir Isaac Newton, Godfrey Kneller, 1702

By Newton’s time, and somewhat because of Newton, scientists were expecting quantitative explanations to natural phenomena. So, several people attempted to use Newton’s ideas to calculate observed results. For example, Newton tried to derive Boyle’s Law involving gases by using forces that decrease in strength as the particles moved further away. In the preface to the Principia, Newton lamented that while he was able to determine orbits of planets, he could only wish that he “could derive the rest of the phenomena of nature by the same kind of reasoning.”

Several others attempted various types of calculations. Some involved large numbers of different types of forces or sizes of particle; some even used different sizes of spaces between the particles. Nothing was considered very successful.

In 1744, Pieter van Musschenbroek (1692-1761), a well-known researcher in electrical phenomena, wrote, “Though there may be several internal principles acting in bodies in different proportions at different distances yet it is impossible to determine them.” Thus, many in the scientific community felt that trying to understand matter by using forces between small particles was not productive.

Generator built by Francis Hauksbee

Generator built by Francis Hauksbee. From Physico-Mechanical Experiments, 2nd Ed., London 1719

At the same time, other ideas were taking hold that did seem productive, at least on the short run. Francis Hauksbee (1660-1713) discovered that heat and electricity could pass through a glass container that had the air removed from it. This observation led Newton to speculate that all of space was filled with an undetectable material that was the medium for the transmission of things like heat and electricity. This idea in turn gave rise to a concept that heat and electricity, among other phenomena, were themselves some type of liquid. When an object increased in temperature, a fluid flowed into it. Likewise, objects with positive electric charge had gained some type of invisible fluid. (A small aside: The idea of two types of electricity was first described by Benjamin Franklin, who was better known as a politician and womanizer.)

While these fluids were not consistent with our modern models, they allowed the scientists of the 18th century to be more quantitative than they could be with Newton’s forces acting on the small objects in matter. Thus, they became popular.

 Georg Ernst StahlMeanwhile, chemists were finding ways to deal with their new experimental results. A German chemist, Georg Ernst Stahl (1659-1734), proposed that chemists use the properties of chemical elements to try to explain their observations. (The word element was not used then, but it is an easy way to get the idea across.) The properties of substances made of more than one element could be determined by the constituents of the substance. This type of effort led to chemists being able to “understand” how different chemicals combine. Because it proved quite useful in the laboratory, this approach displaced using forces to try to explain chemical reactions.

Thus, chemistry and physics went separate ways. Physicists went in the direction of trying to understand heat, electricity, magnetism, and other macroscopic phenomena (and eventually dumped the ideas of invisible fluids). Chemists studied the behavior of gases, chemical reactions, and so forth. These chemical studies did lead to a greater understanding of the small objects that make up matter. So, we will start taking a closer look at them next time.

Images via Wikimedia Commons, public domain


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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.

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