Month: February 2024

The invention of the Leyden Jar marked a significant moment in this history of electrical engineering. The Leyden Jar can be thought of as the first electrical capacitor – a device that stores and releases electrical energy.

The Invention of the Leyden Jar

During the 18th century the mysterious phenomenon of electricity was becoming a hot topic among learned men of science. Electricity could only be created and observed in the moment. One of the mysteries to be solved was whether electricity could be stored for later use and how to accomplish it. The invention that solved the mystery became known as the Leyden jar, named after the city of an early inventor of the device.

The Leyden Jar is typically credited to two individuals, who independently came up with the same idea.  In Germany, Ewald Georg von Kleist was experimenting with electricity.  He was attempting to store electricity with a medicine bottle filled with water and a nail inserted through a cork stopper.  He charged the jar by touching the nail with an electrostatic generator, and he assumed that the glass jar would prevent the electricity from escaping.  While holding the glass jar in one hand, he accidentally touched the nail and received a significant shock, proving that electricity was indeed stored inside the jar.  

Von Kleist experiments were not well known and around the same time another man experimenting with electricity named Peter van Musschenbroek, of Leyden, Netherlands, also stumbled upon the same invention.  Musschenbroek’s device was much like von Kleist’s jar.  It consisted of a glass jar filled with water that contained a metal rod through a cork sealing the top of the jar.  The outside of the jar was coated with a metal foil.  When an electric charge was applied to the metal rod it was found that electricity could be stored in the jar.  Unfortunately for the person touching the metal rod, a significant shock was received. As Musschenbroek recorded what happened when he first touched the rod:

Suddenly I received in my right hand a shock of such violence that my whole body was shaken as by a lightning stroke…. I believed that I was done for.

It didn’t take long until Musschenbroek’s Leyden jar being used and improved by others.  In 1746, the following year, the English physician William Watson improved the jars storage capacity by coating both the inside and outside with metal foil.  Also that same year, the French physicist Jean-Antoine Nollet discharged a Leyden jar in front of the French King Louis XV.  During the demonstration, Nollet arranged a circle of 180 Royal Guards, each holding hands and he passed the charge from the Leyden jar through the circle.  The shock was felt almost instantaneously by all members of the Royal Guard, to the delight of the King and his court.  Demonstrations such as this brought widespread attention to the exciting new field of electricity.  

Impact and Legacy of the Leyden Jar

Prior to the invention of the Leyden jar, electricity could only be observed and experimented at the moment it was created.  The Leyden jar changed this by allowing scientists to store electrical energy and use it when needed.  Researchers could now conduct various experiments related to electric discharge, conductivity, and other electrical phenomena.  As an added bonus, the jar was easily transported, especially compared to the electrostatic generators of the day.  The jars could be linked together to provide additional storage capacity.  These abilities contributed to the growth of knowledge in the field of electrical science.  

For one example, the American scientist and statesman Benjamin Franklin famously used the Leyden jar during his kite experiment in 1752.  In that experiment, Franklin flew a kite during a lightning storm in an attempt to prove that lightning was a form of electricity.  He attached a metal key to the end of the kite, and the key was then connected to a Leyden jar.  Despite some popular accounts of the experiment, lightning likely never struck the kite directly or else Franklin would have been killed. However, he was able to observe that the Leyden jar was being charged, thus proving the electric nature of lightning.  

The Leyden jar is also considered the first electrical capacitor, which today is a fundamental component in modern electric circuits.   The invention of the Leyden jar laid the groundwork for the development of more sophisticated capacitors.  While they briefly feel out of use after the invention of the battery, the basic idea of the Leyden jar capacitor found a renewed use at the end of the 19th century in modern electronic devices, albeit in a much smaller form. 

Overall, the Leyden jar played a pivotal role in the early explanation and understanding of electricity.  Its impact can be seen in the subsequent development of electrical technology and science.  

Continue reading more about the exciting history of science! 

The neutron was discovered by the British physicist Sir James Chadwick in 1932, marking a pivotal moment in the understanding of atomic structure. It was, in a way, the culmination of a series of scientific investigations of the subatomic particles of the atom that spanned several decades. The identification of the neutron provided answers to questions about the mass of the atom, ultimately leading to important developments in nuclear physics.

Developments that Led to the Discovery of the Neutron

In 1897, J. J. Thompson discovered the electron, a subatomic particle with a negative electrical charge. This discovery provided the evidence that atoms were composed of smaller particles. Two decades later, Ernest Rutherford discovered the proton, a subatomic particle with a positive electrical charge. Rutherford proposed a model of the atom with a dense, positively charged nucleus at its center, orbited by negatively charged electrons. However, this model presented a problem. The positively charged protons in the nucleus should all repel each other, causing the nucleus to burst apart. Yet, this did not happen as the nucleus is obviously stable, and the reasons for this stability were not understood at the time. The existence of a neutral particle was postulated by Rutherford as early as 1920.

The Discovery of the Neutron

This discovery of the neutron was the culmination of a series of successive experiments, worked out by several scientists in the late 1920s and early 1930s. In Germany, Walter Bothe found that beryllium exposed to alpha particles produced a new form of radiation. Bothe attempted to explain this sradiation in terms of gamma rays, because it was not deflected by either electric or magnetic fields. All known particles at the time (electrons and protons) contained a charge.

Taking this information a step further, the French husband-and-wife team of Irene Joliot-Curie (the daughter of Pierre and Marie Curie) and Frederic Joliot reported results from an experiment in January 1932 that led to to neutrons discovery. In the same vein as Bothe, their experiment involved the bombardment beryllium by alpha particles. They noticed that the radiation could eject protons from hydrogen-rich substances such as paraffin.  This was puzzling because gamma rays should not have enough energy to be able to knock out protons in this manner. In other words if this unknown radiation was indeed gamma rays then the law of conservation of energy was being violated.

Back at the Cavendish Laboratory in Cambridge, James Chadwick, a college or Rutherford, quickly became interested in these results.  Chadwick and Rutherford had been working on and off over the past decade in identifying the missing neutral particle suspected to be in the atomic nucleus.  This background allowed Chadwick to move quickly.  He also conducted a series of experiments where he bombarded light elements, such as beryllium, with alpha particles.  He noticed the same radiation being emitted which was not deflected by electric or magnetic fields.  However he interpreted the results differently than the others who conducted similar experiments. His observations led him to correctly conclude that the radiation was composed of uncharged particles. He used the laws of conservation of momentum and conservation of energy to calculate that the neutron has a mass similar to that of a proton.  He presented this as evidence of a new subatomic particle, which he detailed in a paper published in 1932 and named the neutron.  For his work he was awarded the Noble Prize in Physics in 1935.  

Impact of the Neutron’s Discovery

The discovery of the neutron was a key piece of the puzzle that allowed scientists to understand the binding energy of the atomic nucleus.  It had enormous impacts in both applied and theoretical physics.  

The discovery of the neutron explained the missing mass in atomic nuclei.  This in turn helped to explain the existence of isotopes – variants of elements with the same number of protons but different atomic weights – and therefore different numbers of neutrons in the atomic nuclei.  It also advanced the understanding of radioactive decay processes.  

The most important impact of the discovery of the neutron was in nuclear physics.  The neutron – a particle without an electric charge – was the crucial component in the development and study of nuclear fission, which occurred in 1938 by Otto Hanh and Lise Meitner.  The development of nuclear fission was quickly applied the development of nuclear energy and weapons.  The neutron plays the key role in the chain reactions that occur in both nuclear reactors and atomic bombs.  It is probably fitting then, that James Chadwick was placed as head of the British team that work on the Manhattan Project that produced the world’s first atomic bomb. 

Beyond nuclear fission, the discovery of the nucleus aided in our understanding in the nuclear processes that power the stars through the process of nuclear fusion.  The study of this process had advanced our understanding on the origins and evolution of the elements.  

Continue reading more about the exciting history of science!