More on Jemmy Jessamy from Infoplease:

• Jemmy Jessamy - Jemmy Jessamy (A). A Jack-a-dandy; a lady's foundling, “sweet as sugar-candy.” ...
• Jack-a-Dandy - Jack-a-Dandy A term of endearment for a smart, bright little fellow; a Jemmy Jessamy. Smart she is, ...
• Jemmy - Jemmy a name found in engravings of the eighteenth century, was James Worsdale, the painter and ...
• Dictionary of Phrase and Fable: J - Definitions, origins, and illustrative excerpts for words, phases, and literary allusions starting with "J"