Then there were a number of books.
"Elementary textbooks," said Dr.Farnsworth, glancing at them.

On the flyleaf of one of them was written in a bold, firm hand: "Logan Black." "Loge--or Logan Black," said Dr.Farnsworth, "has been giving himself an education in the manufacture of high explosives." "But THESE aren't textbooks," said Lady Agatha, who had pulled out three long, narrow volumes from the pile.

"They're in manuscript, and they look more like account books." The first of them, in Loge's handwriting, contained a series of notes, mostly unintelligible to Cleggett, dealing with experiments in two sorts of manufacture: first, the preparation of counterfeit money; second, the production of dynamite bombs.
The second of the manuscript books was in cipher.

Cleggett might have deciphered it without assistance, for he was skilled in these matters, but the labor was not necessary.

The book was for Loge's own eye.