A type of this field illuminator appears to be referenced in The Telescope, by Louis Bell, 1922, pg 173. These were used to illuminate the spider lines (cross hairs, or reference line) on instruments or eyepieces. These lines were illuminated just enough for them to be seen, or a faint light was diffused in the field and the spider lines would appear darker than the background. The latter seems to be the way the illuminator was used on this telescope.
	The lefthand picture shows the hole in the center tube segment in which the illuminator is mounted. The illuminator is shown in the right hand picture inserted into its holder which is then bolted to the tube.  The faint light is diffused toward the eyepiece by the prism. The prism extends 1 - 1/2" into the tube, while the last aperture stop in the tube is 2 - 1/8" wide. The light then never has a direct path to the eyepiece and is reflected off the front of the stop and the field is faintly illuminated.
	The illuminator removed from the mounting tube and prism. The electrical terminals are on top. Probably a battery was used to light the bulb.
	The prism facing end of the illuminator showing the frosted glass behind which is a small lightbulb.  The rough diameter of the illuminator is 1 - 1/4".
	The lightbulb housing removed from the tube.
	The bulb is marked with a paper lable "5 1/2 - 2"
	The filament is still intact!