@misc{Sylvester_James_Joseph_(1814–1897)_Observations_1908,
 author={Sylvester, James Joseph (1814–1897)},
 copyright={Public Domain},
 address={Cambridge},
 howpublished={online},
 year={1908},
 publisher={Cambridge University Press},
 language={eng},
 type={Text},
 title={Observations on the method for finding the centre of gravity of a quadrilateral},
 URL={http://rcin.org.pl./Content/115398/PDF/WA35_140180_11371-2_Art64.pdf},
}