In this way the scale can be viewed by a microscope of much higher magnifying power than can be employed for the photographed spectrum.
Photographed by Professor C. D.
By the use of photography, however, it is possible to photograph the trail of a star as it transits the meridian when the telescope is directed towards the north, and another trail be similarly photographed when the telescope is directed towards the south.
The adoption of a reseau photographed upon the plate has greatly facilitated the procedure.
Vogel and his successors employed one or other form of measuring machine, provided with a microscope having single or close parallel webs which could be successively pointed on the photographed lines of the star spectrum and the lines of the terrestrial spectrum.