Clifford, William (1878). "Applications of Grassmann's extensive algebra". American Journal of Mathematics. 1 (4): 350–358. doi:10.2307/2369379. JSTOR2369379.
Clifford, William K. 2007 [1870]. "On the Space-Theory of Matter." P. 71 in Beyond Geometry: Classic Papers from Riemann to Einstein, edited by P. Pesic. Mineola: Dover Publications. Bibcode:2007bgcp.book...71K.
Clifford, William (1878). "Applications of Grassmann's extensive algebra". American Journal of Mathematics. 1 (4): 350–358. doi:10.2307/2369379. JSTOR2369379.