Fitz-James O’Brien was born in Cork in 1826 and emigrated as a young man to the USA, where he died in 1862 in Cumberland, Maryland, at age 35.
He is remembered is SF for two short stories.
In the Diamond Lens (1858) a scientist is attempting to develop a perfect microscope to see further into the invisible world than ever before. He is informed in a séance that a high grade diamond when subjected to an “electro-magnetic force” will become a perfect lens.
Obsessed by the idea of such a lens he encounters a man who possess such a diamond and when he refuses to sell it—murders him.
Using the diamond he is able to see more and more minute creatures. However, one day when using his new microscope’s maximum power he sees a strange ethereal landscape in the midst of which is a beautiful woman—though of infinitesimal proportions.
He becomes obsessed with finding a way of communicating with her but one day on attempting to observe her he finds the landscape withered and the miniature woman dying.
He had forgotten to stop the drop from drying out.
Although somewhat ridiculous, this is the first example of an unknown world of minute proportions—later to be revisited by Cummings in his Girl In The Golden Atom.
In What Was It? (1859) a group of friends spend a night at a supposedly haunted house. In the night, one of them is violently attacked. Eventually the creature is captured but is found to be invisible. By taking a cast of it, they determine it to be a short humanoid creature of ferocious appearance. They imprison it and attempt to feed it but it starves to death. They conclude its true food was human flesh. This is one of the 1st uses of invisibility in SF.