Gemini was an iron twin-hulled paddle steamer, the single paddle being between the two hulls. She had twin chimneys and rudders at both ends so she could move in both directions. This image is of the port broadside and the vessel is flying the British flag at the stern and an unidentified pennant on a flag mast mid-ship. Passengers are visible on the decks and there are cabins and deck awnings for their comfort. Several small ketches and another paddle steamer are visible in the scene, as is the land on the horizon.
Gemini was invented and launched by Peter Borrie, at a cost of £14,000. She was intended to carry goods, passengers, cattle and all types of vehicles on the Thames. It was hoped that she would carry a large number of passengers during the Great Exhibition of 1851. However, when tested, she failed to achieve any speed.
(Source: Parker, H. and Bowen, F.C., Mail and Passenger Steamships of the XIXth Century, p.119)