(Click for full photo)
1870 - 1900 Sunbeam rear quadrant rear quadrant from Sunbeam oilbath (part of 1896 patent)
Photo courtesy of Norman Miller, Pa. USA
from Golden Sunbeam 117602, circa 1912
This should be viewed in conjunction with the oil-filler pictures, since it shows the internal arrangements which allow the oilbath to remain oiltight in operation, yet capable of being filled and emptied through the same hole at the rear.
part of patent GB189623149
See the details by keying the number in at ep.espacenet.com/numberSearch?locale=en_ep