Contributions to Molecular Physics in the Domain of Radiant Heat

Abstract

FORTY years ago our knowledge concerning the radiation and absorption of heat was very meagre. We believe that the earliest experiment in this direction is to be found in that wonderful book containing the “Essayes”of the Florentine Academicians. There we meet with the fact that the heat of the sun, converged by a mirror, can ignite a pastile placed within a Torricellian vacuum. A little later, in 1682, Mariotte communicated to the Paris Academy of Sciences that the heat of a common fire, made very sensible in the focus of a burning mirror, was entirely cut off by the interposition of a sheet of glass. The mirror in this case must have been of polished metal. These experiments were subsequently repeated and extended by Lambert, who, assigning the true cause, pointed out the necessity of employing metal, and not glass mirrors, in the reflection of heat from terrestrial sources. Lambert further showed that if the radiation from a clear fire were converged by a large glass lens, no heat was felt where the brilliant focus was seen, whilst Hoffmann first collected the obscure heat of a stove to a focus by a metal mirror.

Contributions to Molecular Physics in the Domain of Radiant Heat.

By John Tyndall (Longmans, 1872.)