A FIVE-METER DOUBLE PASS EVACUATED GRATING $SPECTROGRAPH^{*}$

Abstract

This instrument shows performance comparable to that of the ten meter unevacuated instrument which has been in use in this laboratory for a number of years. At the present time only about 90 $%$of the total optical path (source to detector) is being evacuated. However, it has been possible to work in regions formerly inaccessible to our high resolution unevacuated instrument. Some of the optical and mechanical problems have been solved in a rather novel and satisfactory manner.