Frederick was Frederic’s nephew, and both of them worked at the Plimpton Manufacturing Company, apparently overlapping there. Unfortunately, the Courant regularly added a “k” to Frederic’s name, which means it can sometimes be difficult to differentiate between these two. Fortunately, the Courant tended to refer to Frederick as “F. Plimpton” and Frederic as “F. W. Plimpton,” but it seems likely that I will continue to confuse these two individuals as I move forward in my research.