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. Nearly 25 years later Forbes wrote up his overland odyssey – it was a journey that few seasoned western explorers had made, much less lone travellers in their mid-20s. With contacts made on this journey, Forbes was able to become the only British war correspondent with the Russian army in the Russo-Turkish war of 1877, reporting for The Times. He received the Russian Order of St George for this work.