Three of the earliest recorded observers of the volcanoes were the Scottish scientists Archibald Menzies in 1794, James Macrae in 1825, and David Douglas in 1834. Just reaching the summits proved daunting: Menzies took three attempts to ascend Mauna Loa, and Douglas died on the slopes of Mauna Kea. The United States Exploring Expedition spent several months studying the islands in 1840-1841. American geologist James Dwight Dana was on that expedition, as was Lieutenant Charles Wilkes, who spent most of the time leading a team of hundreds that hauled a pendulum to the summit of Mauna Loa to measure gravity. Dana stayed with missionary Titus Coan, who would provide decades of first-hand observations. Dana published a short paper in 1852.