Tyndall explained the heat in the Earth's atmosphere in terms of the capacities of the various gases in the air to absorb radiant heat, a.k.a. infrared radiation. His measuring device, which used thermopile technology, was a significant early step in the history of absorption spectroscopy of gases. He was the first to correctly measure the infrared absorptive powers of the gases nitrogen, oxygen, water vapour, carbon dioxide, ozone, methane, etc. He concluded that water vapour is the strongest absorber of radiant heat in the atmosphere and is the principal gas controlling air temperature. Absorption by the bulk of the other gases is negligible. Prior to Tyndall it was widely surmised that the Earth's atmosphere has a Greenhouse Effect, but he was first to prove it. The proof was that water vapor strongly absorbed infrared radiation.