  We conduct a series of experiments with a special interest on a penetration
process and instabilities arisen on a liquid jet impinged to a liquid of the
same kind flowing in a channel. The impinged jet penetrates into the flowing
bath accompanying with entrainment of the ambient immiscible gas, which results
in the impinged jet wrapped by the entrained gas as a 'sheath.' This sheath
formation enables the impinged jet to survive in the fluid in the channel
without coalescing until the entrained-air sheath breaks down. Occasionally a
'cap' of the entrained air is formed at the tip of the penetrated jet, and the
jet elongates like a long balloon.
