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We have developed a pressure scanning cold Fabry-Perot spectrometer for the study of the warm diffuse component of the interstellar medium. In order to reduce thermal background and increase sensitivity optical components are cooled to 77K in a LN$_2$ cryostat. Wavelength scanning is accomplished by changing N$_2$ pressure in the etalon chamber. The instrument can be scanned over its free spectral range of 300$km\;s^{-1}$, and it has a velocity resolution of 20$km\;s^{-1}$. A high performance InSb photodiode is used with an integrating preamplifier.
This instrument, with its high spectral resolution and large field of view ($\approx$ 1$^o$) is well suited for observation of line emission from extended low surface brightness objects. Its design has been developed to allow detection of the diffuse Brackett-gamma and Brackett-alpha emission lines from the warm ionized component of the ISM.
