The Electric Disc: Machines for Exciting Frictional Electricity

Patent

The intention of the improvement was to pare down the size and complexity of the plate glass static electricity generating machines used for demonstration and experimentation to its essential, functioning elements that would be cheap and easy to manufacture. These plate glass machines were developed in the 18th and 19th centuries; some could be as large as a room. 

Soon after registering the patent Stanley published a book of experiments, “calculated only to amuse”, but then realised the opportunity to illustrate by example the theory and current state of scientific investigation. 

The other main improvement is in the way that the charge is conducted from the glass. The main feature of a positive friction machine is that a charge builds up on a fixture—the thing that gives you a shock if you touch it when you are grounded. Instead of a metal tube with spikey fingers conducting the charge away from the glass (as in the photo), he substitutes a simple ball attached to a metal screen. So instead of a big machine holding a lot of charge on the device, he provides a small one connected by a chain to a “Leyden jar” (the jar on the table in the drawing) for storing sufficient charge used in experiments that require it. 

In his book Stanley’s Patent Electric Disk and 100 experiments by a Positive Conductor, he states that the experiments are amusing so as to be memorable. They are numbered up to 150 and divided into categories such as attraction/repulsion, effect on the human frame, and the luminous effects of electricity passing through gasses. 

Some experiments are meant to impress, like igniting gunpowder inside a model of a house (exp. 114) or illuminating a fish (exp. 88). Others do things like ring bells or see-saw using the motion of push and pull through the alternating charging and then grounding little hanging wooden pith balls. 

He mentions an experiment by Abbe Nollet where an electric charge through an entire regiment of 1500 men all received a violent shock through the arms and shoulders. There doesn’t seem to be an upper limit to the distance of a static discharge. 

Towards the end of the book, he illustrates more technical aspects: the principles of detecting and measuring the forces applied by the charge; how to distinguish positive from negative charge; “decomposing” water by creating a spark underwater, creating hydrogen and oxygen; making a permanent magnet; making nitric acid from the air; and demonstrating that the charge gathers on the outside surface of bodies only. 

Many experiments involve exciting gasses in a partial vacuum in a glass tube to make them glow. Or exciting coatings like oxide of uranium, which is pale greenish-yellow but brilliant emerald green when electrified. I expect it is human nature to pursue bright and sparkly colours in an era of gaslight. These demonstrations seem to be one step away from neon lights and cathode ray tubes. A little over a decade later, the apparatus and machines at the Crystal Palace Electrical Exhibition would be put on display, showing the magnificent effects of modern invention-the capabilities of the electric light, powers of the telephone, glass insulators and electric sewing machines. 

Towards the end of the book, he illustrates more technical aspects: the principles of detecting and measuring the forces applied by the charge; how to distinguish positive from negative charge; “decomposing” water by creating a spark underwater, creating hydrogen and oxygen; making a permanent magnet; making nitric acid from the air; and demonstrating that the charge gathers on the outside surface of bodies only. 

Many experiments involve exciting gasses in a partial vacuum in a glass tube to make them glow. Or exciting coatings like oxide of uranium, which is pale greenish-yellow but brilliant emerald green when electrified. I expect it is human nature to pursue bright and sparkly colours in an era of gaslight. These demonstrations seem to be one step away from neon lights and cathode ray tubes. A little over a decade later, the apparatus and machines at the Crystal Palace Electrical Exhibition would be put on display, showing the magnificent effects of modern invention–the capabilities of the electric light, powers of the telephone, glass insulators and electric sewing machines.