Julius Sumner Miller: Lesson 38 - Electrostatic Phenomena - Foundations of Electricity

All stuff is electric in nature! Everything is electric! Stones - stars -all living things. For all stuff is made up of atoms - and atoms are made up of charged particles.
A - It was THALES in ancient Greece who first reported the strange behavior wherein amber when rubbed acquired the property of attracting unto itself light bits of straw and dust. THIS was the foundation of all electrical science. So we show these things with a rubber rod rubbed with fur. Cork dust is quickly ''attracted".. AND - quite as important - the dust is soon DRIVEN AWAY. It is very important to UNDERSTAND these actions. Coulomb forces are strong and ever-present.
B - We show similar effects with a pocket-comb We do work by rubbing the comb on something. Charges are separated. Electric energy is thus made available.
C - We define the charge on a rubber rod when it is rubbed with fur as NEGATIVE. The fur therefore has an equal measure of POSITIVE charge. Similarly - a glass rod rubbed with silk has on it - by definition - a POSITIVE charge. To determine the nature of an unknown charge we use an ELECTROSCOPE which we can charge by CONDUCTION or by INDUCTION. The sequence of operations in both is very important. When an electroscope is charged by CONduction the charge on the instrument is that of the charger. When an electroscope is charged by INduction the charge on it is opposite that of the inducer.
D - Pith balls hang on silk strings. They are first electrically or electrostatically NEUTRAL. We now approach them with a charged rod. They flee swiftly to the rod - touch it - hang on a moment - and soon swiftly swing away_ They first FEEL the effects of induction. Then on contact they are charged by conduction. Having now the same charge as the rod they flee from the rod and from each other.
E - And where will an electroscope be unaffected by an electric field?
Answer: in a closed metal conductor - as in a wire cage. And thus we learn what places are safe in a lightning storm.
F - To show how ENORMOUS these electrostatic forces CAN be: Place a long 2 by 4 or a heavy clean plank astride a watch-glass so it can turn freely. Stroke one end of the 2 by 4 swiftly with a cat's fur. Also charge a rubber rod with fur. Now approach the end of the log with the charged rod. It turns! The electrostatic forces are really massive. It is an interesting exercise to compare these electric forces with the gravitational forces.
Finally this must be said: Although the operations we have done in this Lesson seem trivial they are fundamental to the science of ELECTRICITY and indeed constitute the FOUNDATIONS of all electrical science.