The Mont Blanc massif has provided numerous opportunities for academic research, dating back to the very first ascent of Mont Blanc in 1786 during which Michel Paccard carried scientific equipment to confirm it as the highest summit.: In 1820, an ill-fated expedition led by Dr Hamel included pigeons intended for release at varying altitudes to measure the impact of reduced air density on their ability to fly. In 1890, Joseph Vallot built a small meteorological observatory at approximately between the Dôme du Goûter and Mont Blanc's summit from where numerous measurements and scientific experiments were conducted. One study involved taking simultaneous temperature measurements made over many months at Chamonix, the Grands Mulets and at the observatory itself. In 1893, Pierre Janssen constructed an astronomical observatory on the top of Mont Blanc, partially buried within the summit ice to hold it in place. A telescope and a spectrograph for measuring the oxygen content of the sun were installed. The observatory was removed when it started to collapse around 1906.