The first mention of antimatter in a scientific article is in Nature (August 1898!!!). It was a letter to the editor written by Dr. Aurthur Schuester from manchester University... it is an amazing and funny speculative piece on the possibility of anti-matter... It is positively inspiring! I have quoted excerpts of that article in many talks- including the last two that i gave on my job interviews.

One quote that I loved was "Astronomy, the oldest, yet most juvenile of sciences may yet have surprises in store" Given that this was written in 1898 I think it qualifies for the greatest understatement of the 19th century... I quoted his article in my talk to get my current job- and I said that that statement was still just as much an understatement today...