Their correspondence reveals that Niépce was at first reluctant to divulge any details of his work with photographic images. To guard against letting any secrets out before the invention had been improved, they used a numerical code for security. 15, for example, signified the tanning action of the sun on human skin (action solaire sur les corps); 34 – a camera obscura (chambre noir); 73 – sulphuric acid.
Great pic. If a rooster lays an egg on a triangular shaped roof, which way does it roll?