A spark chamber is a particle detector, a device used in particle physics for detecting electrically charged particles. They were most widely-used as research tools from the 1930s to the 1960s, and have since been superseded by more sophisticated detectors such as drift chambers and silicon detectors. Today, working spark chambers are mostly found in science museums and educational organisations, where they are used to demonstrate aspects of particle-physics and astro-physics.
Spark chambers consists of a stack of metal plates, placed in a sealed box filled with a gas such as helium, neon or a mixture of the two. When a charged particle from a cosmic ray travels through the box, it ionizes the gas between the plates. Ordinarily this ionisation would remain invisible. However, if a high enough voltage can be applied between each adjacent pair of plates before that ionisation disappears, then sparks can be made to form along the trajectory taken by the ray, and the cosmic ray in effect becomes visible as a line of sparks. In order to apply this voltage, a separate detector (often containing a pair of scintillators placed above and below the box) is needed. When this trigger senses that a cosmic ray has just passed, it fires a fast switch to connect the high voltage to the plates. The high-voltage cannot be connected to the plates permanently, as this would lead to arc-formation and continual discharging.
As research devices, spark chamber detectors has lower resolution than bubble chamber detectors, but could be made highly selective with the help of auxiliary detectors, making them useful in searching for very rare events.
Streamer chambers are a different type of detector, though closely related to spark chambers. In a spark chamber one looks at a stack of parallel plates edge-on. For this reason, best viewing is afforded when the particle comes in perpendicularly to the plates. A streamer chamber, in constrast, typically has only two plates, at least one of which is see-through (e.g. wire mesh or a conductive glass). Particles come in roughly parallel to the plane of these plates. A much shorter high voltage pulse is used than with a spark chamber, so you don't get breakdown and no sparks are formed. Instead you get streamers (which are sort of pre-sparks which han't yet reached either electrode). These are are rather dim, but can look quite brilliant with some image enhancement (see external links below).
