\noindent In recent years, thick layers of diffuse or warm ionized gas similar to the ``Reynolds'' layer of the Milky Way have been found in several external galaxies. The origin as well as the ionization of this significant component of the ISM are still a puzzle. It is currently unclear whether this gas is related to any of the proposed scenarios of large scale circulation of matter such as galactic fountain flows or just being ionized from OB stars in the underlying disk.
Constraints on the origin of this gas can be expected from kinematical studies. As this gas is best traced by the optical emission lines we have obtained Fabry-Perot imaging spectra at H$\alpha$ of the prototype edge-on galaxy NGC~891. Using TAURUS II attached to the WHT on La Palma we observed two overlapping fields of 5\arcmin \ each in the NE and SW of this galaxy with a velocity resolution of $\approx$ 25~km/sec. Here we present first results of our study.
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