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The Geissler tube is a glass tube for demonstrating the principles of electrical discharge. The tube was invented by the German physicist and glassblower Heinrich Geissler in 1857. The Geissler tube was an evacuated glass cylinder with an electrode at each end. Geissler tubes contain a combination of one of the following: rarefied (thinned) gasses such as neon, argon, or air, or conductive liquids or minerals. When a high voltage is applied to the terminals an electrical current flows through the tube. The current will disassociate electrons from the gas molecules, creating ions and when electrons recombine with the ions different lighting effects are created. The light will be characteristic of the material contained within the tube and will be composed of one or more narrow spectral lines.

They were mass produced from the 1880s as entertainment devices, with various spherical chambers and decorative serpentine paths formed into the glass tube. When the tube was handled (the terminals were insulated) the shape of the plasma changed. Some tubes were very elaborate and complex in shape and would contain chambers within an outer casing. If these were spun at high speed a visual disk of color was seen due to persistence of vision. (Somewhat similar devices in the form of stationary globes are now produced and sold for personal amusement.) As an educational tool they are also used to demonstrate the movement of electrons and the principles of a vacuum.

It was observed that under some conditions that the glass envelope would itself glow at the positive (anode) end. This glow was attributed to the transmission of a ray from the negative cathode at the opposite end of the device, and so were named cathode rays. William Crookes developed a modification of the Geissler tube into what is known as the Crookes tube to demonstrate and study these rays, later determined to be a stream of electrons. This device was further developed into the cathode ray tube with applications in electronics development and diagnosis, and in radar and television displays.

Xenon in shaped neon tubes, a derivative of Geissler tubes.

Geissler tubes have had a large impact on the development of many instruments and devices all of which use related vacuum and discharge principles.

• Xenon flash lamps (for flash photography),
• Xenon arc lamps (for automobile headlights),
• X-ray tubes,
• sodium vapor lamps of low and high pressure,
• "Neon" signs (both using visible light discharge from neon and other gases and indirectly through phospor excitation from ultraviolet light)
• Mercury vapor lamps,
• Mass spectrometry devices,
• Cathode ray tube (employed in the Oscilloscope (an electronic diagnostic device) and later as a television, radar, and computer display device),
• Electrotachyscope (an early moving picture display device), and
• Fluorescent lamps.

People

William Crookes

Devices

Cathode ray tube (CRT), Crookes tube, Induction coil, Neon sign, X-ray tube

• Sparkmuseum: Crookes and Geissler Tubes
• Instruments for Natural Philosophy: Geissler Tubes
• Mike's Electric Stuff: Geissler Tubes
• The Cathode Ray Tube site
• Geissler and Crookes tubes shown working