Bought at a local Flea/Collectors market in Cheltenham England this viewer measures approx 12" x 24" with a height (when folded) of about 4-1/2".
It was (apparently) quite a common viewer in it's day*, possibly due to the fact that it is well suited to table top viewing as a result of its adjustable easel. It is also a very attractive piece of furniture!
It doesn't appear to be particualarily well suited to standard Holmes type mounts as they are a little to wide to fit within the callipers and be fused into a single image by the eye. It does however produce an excellent stereo image from standard 35mm prints when a beam splitter has been used to split the images! There is a transparent area on which tissue mounts can receive some rear illumination and I would guess that this was the more common picture style of the day.
An slightly enhanced version of this viewer was sold at auction last year for 230 GBP (Christies, London).
Rowsell Stereographoscope 2
Another purchase while on Holiday. I spotted this in an antique and collectors shop in Sarasota, Florida. It came as a package with a nice set of stereo cards from Unwin & Unwin (the cards and the scope are not a good match for the reasons already mentioned) . Though not as well made as the other Scope on this page this one does have the large monscopular magnifier which was typical of many stereographascopes of the day. The scope was made to a standard French design* and may well have originated from there. It would have been made around the turn of the century.
Like the other scope on this page the unit folds up nicely into itself for storage.
I was lucky to pick up the scope with cards for $100
* Many different models existed including 'one offs ' made by individual craftsmen to the same basic design.