Burning glasses and a glass-polishing machine. Colored engraving by J. Pass, 1799. Illustration showing methods of creating fire by artificial means. Burning glasses were used in experiments by early chemists. By placing lenses in the sun, angling them towards the substance to be heated, a heat source was created which avoided the need to place an object directly in a fire. The use of burning glasses was first mentioned by Roman philosophers Seneca and Pliny the Elder during the first century AD.