\bib{1761/euler}
\yr 1761
\by Leonhard Euler
\paper Observationes de Comparatione Arcuum Curvarum Irrectificabilium
\jour Novi commentarii scientiarum Petropolitanae
\vol 6
\pages 58--84
\also Enestr\"om 252
\url http://math.dartmouth.edu/~euler/pages/E252.html
\endref