Niels Abel submitted his impossibility proof for the quintic equation in 1824. Because of lack of funds, he was forced to condense his proof to only 6 pages. This greatly reduced the clarity of the proof. Later, in 1826, Abel published a longer version of his proof that provided additional details. Tragically, in 1829, he grew very sick and died. The great work of Evariste Galois would not come to light until the 1840's.
Even in 1833, Abel's proof was not yet fully accepted by all major mathematical bodies. On that year, George Peacock wrote a report for the British Association for the Advancement of Science where he concluded that "some parts of it are obscure, and not perfectly conclusive."
For the English world, any doubts about Abel's proof would go away with the important work by Sir William Rowan Hamilton. On May 22, 1837, Hamilton presented a paper to the Royal Irish Academy which would settle the issue.