"Let's examine it for repetitions first.

Here we have this symbol [Illustration: Cryptographic symbol] repeated five times.

It's likely to be the letter E.I think--" His voice ceased; for a quarter of an hour he pored over the symbols, pencil in hand, checking off some, substituting a letter here and there.
"No," he said; "the usual doesn't work in this case.

It's an absurdly simple cipher.

I have a notion that numbers play a part in it--you see where these crossed squares are bracketed--those must be numbers requiring two figures--" He fell silent again, and for another quarter of an hour he remained motionless, immersed in the problem before him, Harren frowning at the paper over his shoulder..