A. Macfarlane (1893) "On the definitions of the trigonometric functions", page 9, link at Internet Archive
A. Macfarlane (1900) "Hyperbolic Quaternions" Proceedings of the Royal Society at Edinburgh, vol. 23, November 1899 to July 1901 sessions, pp. 169–180+figures plate. Online at Cambridge Journals (paid access), Internet Archive (free), or Google Books (free). (Note: P. 177 and figures plate incompletely scanned in free versions.)
A. Macfarlane (1900) "Hyperbolic Quaternions" Proceedings of the Royal Society at Edinburgh, vol. 23, November 1899 to July 1901 sessions, pp. 169–180+figures plate. Online at Cambridge Journals (paid access), Internet Archive (free), or Google Books (free). (Note: P. 177 and figures plate incompletely scanned in free versions.)
cambridge.org
journals.cambridge.org
A. Macfarlane (1900) "Hyperbolic Quaternions" Proceedings of the Royal Society at Edinburgh, vol. 23, November 1899 to July 1901 sessions, pp. 169–180+figures plate. Online at Cambridge Journals (paid access), Internet Archive (free), or Google Books (free). (Note: P. 177 and figures plate incompletely scanned in free versions.)