His working assumption was that the particles were normal atoms which had become charged by the high voltage. Ampere’s work led Crookes to conclude that cathode rays were indeed negatively charged particles. This method coudn't be used at the time.īack in 1820 Andre Ampere had greatly added to ideas about how magnets affected electricity. If the electromagnet is set up as a pair of Helmholtz coils then you can use a fine-beam tube to calculate the charge to mass ratio of the cathode ray particles. You can also bend cathode rays using an electromagnet. You can move the magnet back and forth, and flip it round. Simulation of using a magnet to deflect the green glow in a Crookes tube. When it hit the end of the tube then for some reason it made the glass glow. There seemed to be an invisible ray that could travel through the empty space between the few air atoms that remained. But the glass itself at one end of the tube glowed green. This time there was no glow throughout the gas. He invented an even better vacuum pump than Geissler and managed to reduce the pressure even more. One of the many scientists interested in Geissler tubes was the Englishman, William Crookes. There must have been some air left in and for some reason it glowed with a high voltage across it. There is a glow which fills most of the tube. Let’s just recall what we saw when most of the air was sucked out by Geissler. By the 1880s a huge variety of Geissler tubes were mass produced and people bought them because they were amusing and pretty. He found that some liquids glowed in his tubes and by using different gases he could get different colours. The best models of this kind of coil were designed by Heinrich Ruhmkorrf, a German instrument maker who set up in Paris in the 1850s. Since coils act as electromagnets you can use one of the coils to automatically make and break the circuit very rapidly. Could you still get sparks if there was no air?įor example you could get sparks by winding two coils of wire over each other and then making and breaking a circuit in the shorter coil. There was no really good core theory to guide research so at first scientists spent a lot of time just trying out new stuff. Was it a bit like light? Or a particle? Or something completely different? No one really had a clue what electricity was. This meant scientists could see the effect of electric currents without having to use static electricity from rubbing two materials together. In 1800 the Italian scientist Alessandro Volta had invented the first electric battery. The invention of the battery made it easier to study electricity
But research grants, narrow specialism and peer-reviewed work did not become widespread until the 1950s. Scientists would discuss their research at places like the Royal Institution and there were a number of learned journals.
Graphic James Parsons (1800 - 1867), 3rd Earl of Rosse, built what was for decades the biggest telescope in the world. The judge sentencing him said ‘The Republic has no need of geniuses’. He was tried as a traitor by a revolutionary court, convicted and executed by guillotine all on the same day. You needed to be rich to be a scientists so many scientists were also nobles, like Antoine Lavoisier, the father of chemistry. And in 1789 The French Revolution saw ordinary citizens violently seizing power from the French King, Louis XVI and his nobles. So in 1776 Thomas Jefferson drafted the United States Declaration of Independence. People wanted to control their own lives. Also being abandoned were the ideas that a small number of very rich families should always be in power. Remember we saw how science really took off in the ‘Enlightenment’ of the mid 1700s, where Aristotle’s ideas were increasingly abandoned. Science was only a small part of the Enlightenment And in lesson 9 we’ll look at how scientists came to the conclusion that atoms must be mostly empty space with a tiny nucleus at their centre.
In this lesson we’ll see how scientists during the late 19th and early 20th century developed ideas about electrons being part of an atom.