21 OCTOBER 1865, Page 21

Radiation. By John Tyndall, F.R.S. (Longman.)—This is one of Professor

Tyndall's lucid papers on a scientific subject, delivered as the " Redo Lecture " before the University of Cambridge. That heat is nothing but motion—that radiation is the communication of a vibratory movement to the ether, that waves of ether thus generated strike against the molecules of a body, and that by the motion thus trans- ferred the body becomes hot—that in this way all the phenomena of heat Fe reducible to interchanges of motion—are ideas that one may have conceived in a hazy way. After reading the account of the ex- pariments detailed in this lecture, and the reasoning founded there- upon, one feels that one really understands the theory, and that one is beginning to discern the general relationship of natural phenomena.