Shown is a 50,000 volt Ruhmkorff coil, which is a modern version of the device. I use this one for demonstrations rather than my antique Ruhmkorff coils. This device, when hooked to approximately 12 volts DC, can yield 50 kV, which can produce a spark across a 1 inch gap. I use this device to power the Geissler and Crookes tubes in the collection.

A Geissler tube is a type of gas discharge tube used to demonstrate the principles of electrical glow discharge. The tube was invented by the German physicist and glassblower Heinrich Geissler in 1857. The glass is evacuated and slightly backfilled with a rarefied gas or vapor. Electrodes are placed such that they penetrate into the gas volume, yet sealed to preserve the integrity of the partial vacuum. When a high voltage is applied between the electrodes, an electric current flows through the tube. The current dissociates electrons from the gas molecules, creating ions, and when the electrons recombine with the ions, the gas emits light by fluorescence with colors characteristic of the element in the tube. The Geissler tubes were novelty items, made in many artistic shapes and colors to demonstrate the new science of electricity. This same technology is what is used for modern neon lamps.

Shown to the left is a set of Geissler tubes backfilled slightly with various different gases. From left to right are hydrogen (H2), helium, argon, neon, nitrogen (N2), and mercury vapor. A Ruhmkorff coil is used to supply 50 kV to the tubes, which you can hear oscillating in the background.

Shown below are a selection of Geissler tubes from the 19th century. These tubes were used for scientific demonstrations or for home entertainment. The fluorescing gas slightly backfilled in the tube was usually argon, although other gases were commonly used. These tubes often had a colorful dyed liquid surrounding the evacuated tube. Some tubes were fabricated from colorful glass, or even fluorescing glass. These examples are operated with the 50 kV Ruhmkorff coil shown above.

Shown to the right is an anode ray tube (also called a canal ray tube). It has some similar features as a Geissler tube, where there is an evacuated envelope with opposing electrodes, and anode and a cathode. The cathode is at the center of the tube with the anode at the bottom. Further, the cathode has multiple perforations in it. The electric field accelerates ions in the gas, which collide with atoms of the gas, knocking electrons off of them and creating more positive ions, a process that continues to magnify the production of positive ions. The positive ions are all attracted to the negative cathode, and some pass through the holes in the cathode, and are called anode rays. As they pass energy to the gas in the upper portion of the tube, the excited gas atoms produce light as electrons fall back to their ground state. The pink streamers are the result. 

A Crookes tube, or cathode ray tube, is a vacuum device with two (or more) electrodes. One electrode serves as the cathode while the another serves as the anode. A high voltage is placed across the electrodes, and electrons  enter the vacuum through thermionic emission from the cathode. The envelope is evacuated such that the mean free path of the electrons is sufficiently larger that the container dimensions, thereby ensuring that electrons do not collide with gas molecules. Consequently, their trajectories are straight lines, unless altered by external magnetic or electrical fields.

The Crookes tube to the left is a replica of the type used by Roentgen when he discovered x rays. It has a fluorescent material coating the the inside of the far end of the tube. The cathode is at the other smaller end, and the anode is located below the envelope. A Maltese cross attached to a glass hinge is located near the fluorescent screen. When electrons strike the fluorescent screen, visible light is produced. If the Maltese cross is erected upwards, then an electron shadow is cast upon the fluorescent screen. Below are several other examples of Crookes or cathode-ray tubes.

Shown above is a magnetic deflection Crookes tube. Electrodes are at each end, with the anode on the left and the cathode on the right. Inside the tube is a slanted fluorescent screen. A slot through a metal screen allow only a thin line of electrons to pass through towards the anode. Electrons striking the screen show this fluorescent line, and a magnet can be used to show the electrons deflecting in in a magnetic field.

Shown is a paddlewheel Crookes tube. The paddlewheel is suspended within glass rails located between the electrodes.When the device is actived with a high voltage (50 kV), the paddle wheel moves towards the anode. At first, it was assumed that this demonstrated that electrons have mass. However, that was wrong. Instead, the device actually works more like the Crookes radiometer. Electrons striking the paddle cause heating, which causes the few gas molecules nearby to expand and move around the paddle to the cooler side. This action of gas expansion at the paddle wheel is what really causes the wheel to spin.

To the left is a heating Crookes tube. Electrons are emitted perpendicular from a surface, and this tube is designed to demonstrate this fact. The cathode is a hemisphere with the focus located on a metal foil suspended in the tube. Under high voltage, electrons are projected onto the foil, and the electron current causes the metal foil to heat up at the focal spot. Most of these demonstration tubes have a hole in the foil where it has been melted through, and this specimen is no exception. In fact, an e-beam evaporator works on this same basic principle.