A quotation by P G Tait
Perhaps to the student there is no part of elementary mathematics so repulsive as is spherical geometry.
Article on Quaternions Encyclopaedia Britannica (1911)
In future times Tait will be best known for his work in the quaternion analysis. Had it not been for his expositions, developments and applications, Hamilton's invention would be today, in all probability, a mathematical curiosity; and there are those who think that, now Tait is gone, such will ere long be its fate. But I venture to think that Hamilton himself will prove the better prophet: for he wrote to Tait: "Could anything be simpler or more satisfactory? Don't you feel, as well as think, that we are on the right track, and shall be thanked hereafter? Never mind when."
Alexander Macfarlane, Peter Guthrie Tait, his life and works, 1903