They were written by scientist Smithson Tennant, who lived in the 17th and 18th century.
We were lucky enough to see his original letter during a visit to the archives at The Royal Society.
This year marks 250 years since Tennant's birth and Professor Martyn Poliakoff will be giving a public talk as part of the commemorations.
Here's the video we made during our visit:
Professor Poliakoff had a few interesting observations about the documents.

But most interesting were Tennant's descriptions of why he chose the names - due to the appearance and odour of his discoveries.
The video also has a sad and mysterious post script.
The Royal Society archivists showed us a letter outlining Tennant's demise in a horse riding accident.
And how Tennant may have taken another discovery with him to the grave.
More photos from our visit can be found at this link.
And here are details about Profesor Poliakoff's upcoming talk.