“The Fifth Race” is episode fifteen of season two of Stargate SG-1.
When SG-1 went through the stargate in “The Torment of Tantalus”, looking for a professor who had vanished into it decades previously, they discovered a castle with evidence of four different races, including the Asgard, who had apparently used it as a meeting point.
A probe sent through to a new planet has discovered language from one of the races from there. When SG-1 travels to the new planet, O’Neill looks into a device on the wall and passes out.
After he comes around, he occasionally says words in an unfamiliar language. The incidences grow more frequent, and Jack seems to be gaining new mental powers, and acquiring new knowledge.
I think this was a device that was referred to frequently in Stargate: Atlantis. This may also be the first mention of the race known as the Ancients, as well as being the first time the eighth chevron has been used.