@article{1761-euler
,note={URL: {\tt http://math.dartmouth.edu/~euler/pages/E252.html}. Note: Enestr\"om 252}
,author={Leonhard Euler}
,journal={Novi commentarii scientiarum Petropolitanae}
,pages={58--84}
,title={{Observationes de Comparatione Arcuum Curvarum Irrectificabilium}}
,volume={6}
,year={1761}
}