Classified abstracts 4264-4273 width of the energy distribution curve, ranging from about 50 to 15 eV FWHM, is found to depend on the applied voltage VA and the length-to-diameter ratio (+ of the channel, and to vary with output current. The results can be explained in terms of the normalized field strength near the output end of the channel and generalized by a set of universal curves presenting the energy width as a function of output current level for different values of VA/a. (Japan) N Koshida and S Yoshida, Rev scienf Instrum, 50 (2), 1979, 177-180. 34 4264. Construction, adjustment and performance of a 6.600 m grazing incidence vacuum spectrography. (GB) The design, construction and adjustment of a grazing incidence vacuum spectrograph is described. The instrument is adapted to a 6.600 m concave grating with 1200 grooves mm-' and a ruled area 80 mm x 20 mm. The grazing angle is 5". The plate holder covers a wavelength range of O-60 nm. A peculiar deviation of the focal curve from the Rowland circle is discussed. The lower limit of the grating reflectivity corresponds to approximately 3.5 nm. Resolution is better than 90% of the theoretical value, but this could not be checked in the region below 30 nm because of lack of close lines. Improvements in the sliding spark technique are reported. (Netherlands) F G Meijer, J P/I~s E: Scienr fnsfrum, 12 (2), 1979, 129-135. 34 4265. Vacuum ultraviolet wavelength comparison of two copper sources using an imaging system. (GB) Two very narrow CuII lines from a liquid-nitrogen-cooled hollowcathode lamp have been studied with the source imaged by a toroidal mirror on to the entrance slit of a high-resolution spectrometer. The wavelengths from two sources were compared with a precision of *3.5 fm (0.035 mA) in A 205 nm and &2 fm in X 154 nm. The variation of wavelength with pressure above 330 Pa (2.5 torr) and with current between 70 and 500 mA was less than f IO fm. Intensity variations across the cathode were observed and found to be pressuredependent. These can lead to instrumental wavelength shifts of more than IO fm if the source is not imaged. G H C Freeman and W H King, J Phys E: Sri Instrum, 12 (4), 1979, 282-285.