let the pirate bumper pass - a bumper is a cup filled to the brim, as for a toast
scuttling a Cunarder - sinking a passenger ship of the Cunard line
cutting out a White Star - separating a passenger ship of the White Star line from the surrounding ships to capture it (the Titanic was a ship of the White Star line)
on breakers always steering - always making mistakes and getting into trouble
the glass is rising very high - a barometer (rising indicates fair weather)
your pirate caravanserai - as "caravanserai" is a sort of inn for caravans
Wards in Chancery - minors under the protection of the Court of Chancery
from Marathon to Waterloo - the messenger died after running 26 miles to Athens with news of a Greek victory at Marathon. Napoleon's final defeat was at Waterloo.
beings animalculous - an animalcule is a microscopic animal
Sir Caradoc - a Knight of the Round Table
I answer hard acrostics - a parlor game similar to charades, with acted-out words, whose first letters then spell out the real message to be discovered.
I quote in elegiacs all the crimes of Heliogabalus - even the use of a verse form (elegiacs) could not soften the awful deeds of this most appalling Roman emperor
In conics I can floor peculiarities parabolous - conics is the study of cones cut by imaginary planes, producing parabolas, ellipses, and hyperbolas. To floor is to defeat (as in wrestling). Parabolous is Gilbert's adjective variant of parabolic.
I can tell undoubted Raphaels from Gerard Dows and Zoffanies - three painters, from three different centuries and countries, and with quite distinct styles.
the croaking chorus from "The Frogs" of Aristophanes - a comedy produced in Athens in 405 B.C. (the croaking chorus goes "Brekekekex, ko-ax, ko-ax")
whistle all the airs from that infernal nonsense Pinafore - H. M. S. Pinafore was the Gilbert & Sullivan show which preceded Pirates. It was their first great success.
pinafore - a sleeveless usually low-necked apron or dress fastened in the back
a washing-bill in Babylonic cuneiform - a laundry-list in ancient writing
every detail of Caractacus 's uniform - Welsh king who resisted the Roman invasion of Britain had a limited uniform consisting of blue dye... and nothing else
mamelon and ravelin - terms for strategic earthworks: mamelon is a mound used in fortifications, ravelin is a sort of ridge
has never sat a gee - never ridden a horse ("gee-gee" being a childish way of referring to a horse, derived of horse word commands "gee"=left, "haa"=right
Divine Emollient! - something that softens, as poetry apparently does
dimity - a sheer usually corded cotton fabric of plain weave in checks or stripes the family escutcheon - shield displaying heraldic insignia; family crest
threatened with emeutes - a French term for riots or brawls
when the coster's finished jumping on his mother - costermongers (street vendors of fruit, fish, etc.) were sometimes rather rough characters
life preserver - a stick or bludgeon loaded with lead, intended for self-defense, but all too often used by evil-doers (as in this case)
unshriven, unannealed - without having made confession or received last rights
with humbled mien - manner, or general bearing
Central Criminal Court - The Old Bailey-the most famous court in the world
House of Peers - the House of Lords, one of the two Houses of Parliament.