 In Pitlochry he returned to an earlier interest, from 1906 to 1930 delivering the David Elder lectures on Astronomy at the Royal Technical College in Glasgow.For the 1874 Transit of Venus, Forbes was lead astronomer at the Hawai'i sub-station, part of the larger expedition to the Sandwich Islands led by Captain George Lyon Tupman.He returned to Scotland via Peking and St Petersburg, crossing the Gobi desert and Siberia in 1875.