What is This Optical Instrument ?

[msfarrar]

Looks like the disk can be rotated slowly by turning the handle. 
And that whatever is on the disk can be viewed through the eyepiece ?

What is it The picture was taken somewhere around 1900-1910 I think 

[mckha489]

Do you know who the man is?
What was his occupation?
Hobbies?

There is a mirror strategically placed on the table, no doubt directing light through the disc.
I think the crucial question is, what is the disc?
Thoughts so far - Is it a thin piece of rock/stone?

[Erato]

Or maybe a soil sample.  Looking at pictures of antique microscopes, I haven't found anything like it yet.

[mckha489]

I wondered about a spectrometer, but they are not right.

[youngtug]

Could it be some form of Phenakistoscope with a viewing "scope"
That is if it is one item, not two.

[Mike in Cumbria]

I think it can only be a microscope, although I can't find any images quite like this. I found a few similar, but not quite the same.
By 1910, microscopes looked pretty similar to the type we used at school, so I wonder if he's demonstrating a much earlier instrument -hence the photo.

The disc could be a glass plate, on which he's grown some bacteria or fungi.

[Mike in Cumbria]

Hooke's microscope was rather similar.
https://blog.sciencemuseum.org.uk/wp-content/uploads/2015/09/SSPL_10447127_Comp.jpg

[Gadget]

He looks very like William Henry Perkin of purple fame:

https://www.vox.com/science-and-health/2018/3/12/17109258/sir-william-henry-perkin-google-doodle-birthday-180-mauveine-purple-dye

It could be just his beard though 

[msfarrar]

Its a photo of an uncle of my great grandmother.  I don't know his occupation...  Sorry I can't tell you any more.