Geissler developed for the exhausting process a new mercury vacuum pump which he presented in September 1857 at the University of Bonn. With this pump he was able to reach very low pressure levels. These low pressure levels played a very important role in the discovery of cathode rays, canal rays and X-rays in the years that followed. Geissler was not only the maker of the tubes but did also the preparations and research on this new light phenomena. The high tension needed to discharge the tubes came from a Ruhmkorff coil, also a new developed instrument those days by Daniël Ruhmkorff in 1850. This instrument produced a reliable high voltage, in contrast to the static machines, which good working depended on a low air humidity. In 1864 Geissler demonstrated his tubes and vacuum pump for public.

He produced many different tubes, working together with Julius Plücker who called the tubes "Geissler tubes", although similar tubes were made earlier. Heinrich Geissler experimented with different sizes, glass sorts, gas vapors, liquids and pressures. The first years were difficult because the technique of good glass sealing's around the electrodes had to be developed, good quality of glass over a longer period was not easy to obtain due to different manufacturers and incompatibility of their glass. Plucker noticed blackening of the inside tube near the electrodes, Geissler discovered that a thin glass rod around a large part of the electrode prevented this, it is described in the Annalen der Physik 1858. Many early tubes didn't kept the low pressure over time and went useless. A small layer of lead glass sealing around the metal electrodes solved this problem, this was called "einsmeltszglas".
Probably to distinguish the lead glass in the production from the soda lime glass which was used for the tube the tiny bit of lead glass was colored blue (with Cobalt oxide pigment) but also red or green is known, platinum wire was used due to the similar expanding coefficient as the glass.

Tubes from his workshop went soon to other country's like France and England, to researchers like Faraday, Crookes and Hittorf which he sent 50 tubes for research in 1858, the experiments which followed led to a lot of new discoveries.
Heinrich Geissler was honored in 1868 with a promotion of the Philosophic faculty from the University in Bonn. In the meantime Geissler produced many very attractive tubes in different shapes, some with colored fluid fillings or uranium glass. These were not always were used for research but also for commercial entertainment. This gave him some critics from other researchers like Poggendorf in 1867 who believed only in pure scientific work. Nevertheless Geissler gained the production of these attractive tubes and sold them in many countries. Franz Müller joined the workshop of Geissler in 1874 and succeeded the firm in Bonn into the early 20th century as "Geissler's Nachfolger".

Heinrich Geissler died 24 of January 1879 in Bonn at the age of 65 just before the great breakthrough of vacuum tube technology by William Crookes.

This summary is composed from many sources on the Internet.
Annalen der Physik und Chemie.
1857 - Julius Plücker, Heinrich Geißler und der Beginn systematischer Gasentladungsforschung in Deutschland from Günter Dörfel and Falk Müller.
The book Gasentladungsforschung im 19. Jahrhundert  GNT verlag from Falk Müller.
Carl Eichhorn - Heinrich Geissler (1814-1879) His Life, Times and Work  SIS 1990/27
Heinrich Johann Wilhelm Geissler (1814 -1879)

Heinrich Geissler was born in 1814 and raised in the German town of Ingelshieb. His father was like many others in the region of Thuringia a glassblower for making fine glass art like glass pearls. Heinrich Geissler came from a large family, his mother gave birth to 11 children where he was the first child. Four of the children died at a young age due to poor living conditions. As a rule, the children had to work from their fifth year in the family glass workshop where they learned from childhood all the skills needed.

Heinrich Geissler traveled and worked for years through Germany and the Netherlands as an instrument maker before he started in 1852 his own workshop in Bonn for the production of physical and chemical instruments. Here he made instruments for the Physics Cabinet in Bonn were he worked together with Julius Plücker, a Mathematician and Physicist for which he made thermometers and capillary tubes. 

In 1855 Geissler was rewarded with the Gold Medal on the World Exhibition in Paris due to his excellent work on fine glass. In the spring of 1857 Geissler made a sealed glass tube which he exhausted to a low pressure and fitted two platinum electrode connections on each end. He asked Theodor Meyer, an assistant of Plücker to study the stratification effect of the light in the tube.

Heinrich Geisslers brother Friedrich had made earlier these "massonic" tubes (after Masson in Paris who used his Torricellian vacuum tube) for the Dutch Chemists Volkert Simon Maarten van der Willigen in Amsterdam, which were filled with mercury vapor. Heinrich Geissler must be interested in these tubes when he heard of the experiments from his brother in the Netherlands. It was actually a further development of the electrical egg of Jean (Abbé) Nollet (1700-1770) and the experiments of Masson, Grove and Hittorff. His experiments are described in Poggendorff's Annalen vol- XVCIII, page 497, year 1856.

It was the development of the first practical discharge light, a pale bleu/purple light and this new phenomena attracted a lot of other scientist in Europe like Plücker, Gassiot and Crookes. Julius Plucker worked together with Geissler on similar capillary vacuum tubes which Plücker used to concentrate the light for his spectral research.
Electrical egg [Ganot 1870]
Hittorff experiment [Ganot 1870]
Short biography of Johann Heinrich Wilhelm Geissler
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