Hi, Apo, thanks for the response.
This one does have the swing out condenser. It has an iris just under the top of the condenser.
The horseshoe base is square in section of the pillar, whereas the 40 I found in a catalog had a cilendrical piller.
Does this fit the 30 in your sources?
By 1917, of the 22 microscopes Spencer catalogued( not including metallurgical and low power binoculars) only the 30 and 40 were of that retro design. The tubular body/arm section dates back to the late 19th century. I have a similar designed model with a serial # that dates to before 1910, and at 4 digits , likely 1905 or so.
When you say the condenser swings out , it is just the top section, correct? It slides sideways, once lowered below the stage ...and it focuses on a rack and pinion, correct?
The 40 has the older condenser design that also swings out but on the same vertical shaft that also focuses the condenser with a helical screw controlled by a vertically positioned knurled knob, rather than a horizontal knurled knob attached to a pinion gear.