Image courtesy of Smithsonian's National Postal Museum
At the end of the 19th century, large city post offices were hives of activity as seen in this image. Letter carriers are busy casing (or preparing) their daily mail in large pigeon-hole distribution cases in the top half of the photograph. In the bottom half clerks sort mail by tossing it into the appropriate mail pouch. Clerks needed good eyes and good aim for this job!