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Of the many dates found in Dupont weights (which include 1847, 1848 and 1849 too, which can be confusing...), the year 1815 seems quite common. I guess it was to commemorate the fall of Napoleon Bonaparte and the restoration of the monarchy.
One common feature of Dupont weights is the profile: the weights have relatively straight sides, with little curve under to the base when compared to classic French paperweights, and a thick 'wear rim'. Also, the millefiori set up is usually very low in the dome.
Alan