Definition:Octonion/Historical Note

Historical Note on Octonions
The octonions were discovered by in December $1843$, in the wake of the work he did with  on the quaternions.

However, he never made it into print, and it was who published his own work on octonions in $1845$, hence claiming the credit.

precedent was discovered in $1847$ on the evidence of a letter he had written to on the occasion of his initial discovery of them.