I received a question about the No. 3 Eastman Plate Series C cameras and here is what I could find.
It is a folding camera for 3 1/4 x 4 1/4 inch glass plates and was produced from 1902 to 1904. The camera could also be fitted with a Cartridge Roll Holder to take pics on roll film.
There also is a series D, which has an extra long bellows extension. 1600 cameras were made in each series. Serial numbers start with 501.
See the HCCC site for a description of the model.
The camera is a typical apparatus for the 'serious amateur', the man or woman who wanted to make perfect pictures, not snapshots. The Eastman Plate cameras are well equiped for this. The picture could be focused and composed on the ground glass, which was more accurate than a little reflex finder and distance scale, and the lens panel could be moved up and down and sideways. For an explanation on this, with videos, see this page on my website.
One was sold on Ebay in June, fetching US$ 420. I do not know its condition.