Page 376. " Archimedes said that with a long enough lever "

Archimedes Thoughtful
Public DomainArchimedes Thoughtful - Credit: Domenico Fetti
  Archimedes (287-212 BCE) was a Greek mathematician and inventor. He is recognised as the inventor of the compound pulley, and he defined the principle of the lever.

Page 379. " was marked Handel's Water Music "

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Page 390. " titles like Biggles Goes To Mars and Jack Cade "
Biggles
Creative Commons AttributionBiggles - Credit: kiwinz

Biggles is the hero of a series by Capt. W.E. Johns. James ‘Biggles’ Bigglesworth is a pilot and adventurer.

 Jack Cade led a Kent revolt of peasants and small landowners in 1450 against seizure of land by the nobility.

Frontier Hero could refer to American legend Davy Crockett, a frontiersman of the early 1800s known as King of the Wild Frontier.

 

Page 399. " a scruffy Napoleon with his laces trailing, exiled to a rose-trellissed Elba "

Island of Elba - Spiaggia di Cavoli
GNU Free Documentation LicenseIsland of Elba - Spiaggia di Cavoli - Credit: Civvi
 Elba is an Italian island, best known as the first place of exile for Napoleon Bonaparte after his abdication in 1814.  He escaped after a few months, returned to his army and proceeded to fight the Battle of Waterloo.  After this final defeat, he was imprisoned on the much more distant island of St Helena for the rest of his life.

The journey of a modern hero, to the island of Elba
Public DomainThe journey of a modern hero, to the island of Elba - Credit: Published by J. Phillips