'Oh Thomasina!' Such a drama in a diagram

Arcadia

Last evening I really enjoyed a performance of Tom Stoppard's Arcadia at the Duke of York's Theatre: 

Act I, Scene 2  

'Septimus ... You should no more grieve for the rest than for a buckle lost from your first shoe, or for your lesson book which will be lost when you are old. We shed as we pick up, like travellers who must carry everything in their arms, and what we let fall will be picked up by those behind. The procession is very long and life is very short. We die on the march. But there is nothing outside the march so nothing can be lost to it. The missing plays of Sophocles will turn up piece by piece, or be written again in another language. Ancient cures for diseases will reveal themselves once more. Mathematical discoveries glimpsed and lost to view will have their time again. You do not suppose, my lady, that if all of Archimedes had been hiding in the great library of Alexandria, we would be at a loss for a corkscrew? ...'^ p.20.

 Act II, Scene 3

'Lady Croom We are intruding here - this will not do, Mr Hodge. Evidently, nothing is being learned. (To Noakes) Come along, sir! 

Thomasina Mr Noakes - bad news from Paris! 

Noakes Is it the Emperor Napoleon? 

Thomasina No. (She tears the page off her drawing block, with her "diagram" on it) It concerns your heat engine. Improve it as you will, you can never get out of it what you put in. It repays eleven pence in the shilling at most. The penny is for this author's thoughts. 

She gives the diagram to Septimus who looks at it.' p.74
...
Now Septimus retrieves his book from Thomasina. He turns the pages, and also continues to study Thomasina's diagram. ... 

Septimus Why does it mean Mr Noakes's engine pays eleven pence in the shilling? Where does he say it? 

Thomasina Nowhere. I noticed it by the way. I cannot remember now. 

Septimus Nor is he interested by determinism -------

Thomasina Oh... yes. Newton's equations go forwards and backwards, they do not care which way. But the heat equation cares very much, it goes only one way. That is the reason Mr Noakes's engine cannot give the power to drive Mr Noakes's engine. 

Septimus Everybody knows that. 

Thomasina Yes, Septimus, they know it about engines! 

Pause. He looks at his watch 

Septimus A quarter to twelve. For your essay this week, explicate your diagram. 

Thomasina I cannot. I do not know the mathematics. 

Septimus Without mathematics, then.' p.75.

 
Tom Stoppard, (1993) Arcadia (Playscript), Faber & Faber, pb. ISBN 9780571169344.
https://www.faber.co.uk/product/9780571169344-arcadia/

My text source:
https://collegearts.yale.edu/sites/default/files/attachments/arcadia_by_tom_stoppard.pdf 

^n.b. This was therapeutic, but I still mourn the losses from Alexandria and other libraries ... today.