SECTION VIII - THEORY OF THE ACTINIC ACTION OF THE SOLAR RAYS

Summary

Experiments and hypotheses of Tyndall–Originality of his theory; objections and omissions–Is this theory incompatible with that of a repulsive force?

A new theory of cometary phenomena which has been proposed by Professor Tyndall, one of the most distinguished of contemporary physicists, in our opinion merits special attention. In the first place, because we believe it to be altogether new and original ; and, in the second place, because it is derived, not from à priori conceptions, like so many other theories in astronomy and physics, but from accurate experiments and their interpretation.

The study of the action of radiations upon very rarefied media of gaseous matter first led Professor Tyndall to consider the mode of production of the phenomena presented by the heads and tails of comets. Of the undulations proceeding from any luminous source, such as the sun, some have a purely calorific action ; these are those which have the greatest amplitude or are least refrangible; the undulations which constitute or produce light come next in the order of length of wave or refrangibility; the shortest waves are those which manifest themselves exclusively by chemical action.