Charles Darwin’s cross-writing (technique used for saving paper), from 1828.
My dear Fox,
I am dying by inches, from not having any body to talk to about insects: — my only reason for writing, is to remove a heavy weight from my mind, so now you must understand, what you will perceive before you come to the end of this; that I am writing merely for my own pleasure & not your’s. — I have been very idle since I left Cambridge in every possible way & amongst the rest in Entomology. I have however captured a few insects, about which I am much interested: My sister has made rough drawings of three of them…
Cross-writing it was used mostly in the 19th century. After a page of writing had been completed – or usually after both sides of a sheet were filled in – then the writer turned the page 90 degrees and continued, adding a second layer of text, perpendicular to the first. Cross-writing is surprisingly easy to read, as a reader’s mind naturally tunes out the irrelevant lines. (Further layers of text are possible, at other angles, but this reduces legibility very quickly.)