The first feature of the new engine is its greatly increased ratio of compression, represented by the formula 1-1 over r to the power of gamma minus 1, where r represents the ratio of compression and gamma, dimensions of cylinder's diameter.

37 seconds sound clip from the The 39 Steps (1937) classic radio play.

You can hear this line at 00:51:35 in the radio play.

Quote context

[...]

- Mr. Memory? Mr. Memory, can you hear me?

- Yes.

- Mr. Memory, there's something I'd like you to tell us, please.

- Yes?

- What was the secret formula you were taking abroad?

- Will it be all right my telling you? It was a big job learning it. The biggest I've ever tackled. I don't want to throw it away, sir.

- It will be quite all right.

- The first feature of the new engine is its greatly increased ratio of compression, represented by the formula 1-1 over r to the power of gamma minus 1, where r represents the ratio of compression and gamma, dimensions of cylinder's diameter.

- This device renders the engine completely... silent. The exhaust gases impinging on a series entirely eliminating all sound.

- Am I right? Am I right, sir?

- That's quite right, old chap.

- Thank you, sir. I'm glad it's off my mind. At last.

- Memory? Mr. Memory?

- Richard, what is it?

[...]