Heinrich is a scientist and a scholar, one of the greatest minds of the Austrian-Hungarian Empire around 1880. He studied mathematics, physics and engineering. He patented a few of his ideas and became very rich.
He writes a diary with all his observations, experiments and plans. Some of his ideas and inventions are potentially dangerous for humanity and he knows that. This is why he keeps his diary encrypted in order to protect his thoughts in case the diary is stolen.
He arrives at his lab in the morning and wants to continue his work. A few pages of the diary need to be decrypted - Heinrich needs to read last pages in order to refresh his yesterday's ideas and plans. Decryption of 10 pages shouldn't take more than one hour and it shouldn't require anything more than just paper and ink. He has to encrypt new pages and destroy all the plaintext paper trace in the evening.
What encryption schemes were known in the 19th century?
What encryption would Heinrich use?
I tag this question [military], because I think encryption was mainly used in army those days and military procedures may be a valuable source of knowledge.