The members of the Royal Geographical Society would have just enjoyed a slide show (lantern programme) of images taken on Scott's earlier Antarctic Expedition.
The magic lantern has a concave mirror in front of a light source that gathers light and projects it through a slide with an image scanned onto it. The light rays cross an aperture (which is an opening at the front of the apparatus), and hit a lens. The lens throws an enlarged picture of the original image from the slide onto a screen.
Main light sources used during the time it was invented in the late 16th century were candles or oil lamps. These light sources were quite inefficient and produced weak projections. The invention of the Argand lamp in the 1790s helped to make the projected images brighter. The invention of the limelight in the 1820s made it even brighter, and following that the inventions of the electric arc lamp in the 1860s, and then incandescent electric lamps all further improved the projected image of the magic lantern.
It was also an important invention for the motion picture film and 45mm projector because of its ability to screen moving images. To achieve this, mechanical slides were used to make the images move. This was done using two glass slides, one with the part of the picture that would remain stationary and one with the part of the picture that would move on a disc. The glass slides were placed one on top of the other in an orderly fashion and a hand-operated pulley wheel was used to turn the movable disc. The magic lantern also led directly to Eadweard Muybridge's invention of the zoopraxiscope, which was another forerunner for moving pictures.