@article {637, title = {An Ascent of Popocatepetl}, volume = {V}, year = {1898}, keywords = {ascent, Douglass, Popocatepetl}, author = {Douglass, A.E.} } @booklet {636, title = {An Ascent of Popocatepetl}, year = {1897}, keywords = {ascent, Douglass, Popocatepetl}, author = {Douglass, A.E.} }