With longer plates it is possible to reach resolving powers above 600,000
The Lummer-Gehrcke plate, like echellette grating and all other high resolution instruments, was used exclusively in the study of the fine structure of spectral lines in combination with an auxiliary spectroscope that separated the line to be analysed (monochromator).
The Lummer-Gehrcke quartz crystal plate, since it is transparent up to about 200 nm, was for many years the best dispersive apparatus in high-resolution spectrography in the ultraviolet.
In the two spectroscopes that are presented here, which were made by the same hand and are perfectly identical, the telescope and the plate are arranged on the median line of a rectangular platform (25 x 7 cm) of cast iron painted black held by a column 24 cm in height and by a heavy tripod, both of cast iron painted black.
The telescope can turn by a few degrees around the position at which its axis is parallel to the plate and the axis of the collimator. ...continues