Abstract. An automatic pressure stepping control and re-cycling system for use with a Fabry-Pérot interferometer is described. The latter uses narrow band interference filters to isolate the spectral region of interest (Hβ at λ = 4861 Å) and is scanned over wavelength ranges from 6 to 24 Å units centred on the above wavelength. A pre-selected programme of spectral elements can be sampled with an accuracy to ±1 torr and this corresponds to ±0.002 Å, when nitrogen is used as the control gas. The interferometer is designed to operate at resolutions from 0.25 to 1.0 Å at a finesse of 40 and with corresponding plate separations between 125 and 40 μm.

Print publication: Issue 5 (May 1967)
Received 21 November 1966