William Rowan Hamilton (1805 - 1865)

Time is said to have only one dimension, and space to have three dimensions. ... The mathematical quaternion partakes of both these elements; in technical language it may be said to be "time plus space", or "space plus time": and in this sense it has, or at least involves a reference to, four dimensions.

And how the One of Time, of Space the Three,
Might in the Chain of Symbols girdled be.

Quoted in R P Graves, Life of Sir William Rowan Hamilton