The quark-hunting telescope. Adjustments are being made to the scintillation counters. The black shapes of six of these counters can be seen in the centre of the telescope and above and below them are spark chambers each with four gaps filled with a helium-neon mixture. The counters were arranged so that the plexiglass light guides which carry to the photomultipliers the light, which a charged particle makes in the scintillator, were not in line. This was because a particle of integral charge passing through the light guide gives a light signal of about the same intensity as could be expected from a quark passing through the scintillator. The two could be differentiated by looking at the spark chambers but to reduce the likelihood of unnecessary counts, the light guides were positioned as seen in the photograph.