The analyses of a text #1

The narrator recalls his adolescence.
The narrator's old friend Mr. Micawber who was the clerk for Uriah Heep, the partner of Mr.Wickfield, who is the narrator's great aunt's old friend and a local lawyer, exposed Uriah Heep's illegal deeds, of which there is the misappropriation of great aunt's funds.
Now the narrator's old best friend, a lawyer Traddles and Mr. Micawber is dealing with the affairs.
Agnes is Mr. Wickfield's only daughter.
Trotwood is the narrator.
Chapter 54 Mr. MICAWBER'S TRANSACTIONS
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'Then I am delighted to say,' cried Traddles, beaming with joy, 'that we have recovered the whole money!'
'Don't congratulate me, anybody!' exclaimed my aunt. 'How so, sir?'
'You believed it had been misappropriated by Mr. Wickfield?' said Traddles.
'Of course I did,' said my aunt, 'and was therefore easily silenced. Agnes, not a word!'
'And indeed,' said Traddles, 'it was sold, by virtue of the power of management he held from you; but I needn't say by whom sold, or on whose actual signature. It was afterwards pretended to Mr. Wickfield, by that rascal, - and proved, too, by figures, - that he had possessed himself of the money (on general instructions, he said) to keep other deficiencies and difficulties from the light. Mr. Wickfield, being so weak and helpless in his hands as to pay you, afterwards, several sums of interest on a pretended principal which he knew did not exist, made himself, unhappily, a party to the fraud.'
[David Copperfield by Charles Dickens]
1. I'd like to know if "by whom sold, or on whose actual signature" is the abbreviation of "by whom it was sold, or on whose actual signature it was made.
2. I'd like to know if "it" indicates the "that" clause in blue.
3. I'd like to know if "proved, too, by figures" modifies "it."
4. And I'd like to know what "light" means.
Thank you in advance for your help.