Slang/Quote translation!

Hi everybody!!

I would like you to give me your opinion on a quote I found in a novel!! It's a kind of interview between a broadcaster and a composer...

Broadcaster: 'Did you read Lambourn's article about you?'
Composer: Was it a long article? Do you know what Joseph Conrad said about reviews and articles? "Dear boy, I only ze measures zem"' [...]

Here you go... I'm completely lost, i can't make head nor tail of it! I thought it could be sort of Cockney slang... something like "Dear boy, I only the measures them?" But even like this it doesn't make sense whatsoever!? Does it?

I tried to look for quotes by Joseph Conrad but it's been impossible to find this particular one!!

What should i do? What do you think i could translate that into Spanish?