1894. TYNDALL. 15 



can be seen. Some of his most interesting results with radiation 

 were in connection with its meteorological influence. Thus he 

 showed that the effects ascribed by de Saussure, Hopkins, and others 

 to the atmosphere, really result from the aqueous vapour in it, 

 which forms the blanket protecting the earth from excessive cold at 

 night. His study of the atmosphere in this connection subsequently 

 came in usefully during his elaborate experiments on fog-signals. In 

 relation to the same subject, he was led to study the effects of the 

 floating particles in the air, and he showed that the blue of the sky, 

 of the Alpine lakes, and of the sea is due to the polarisation caused 

 by these particles. He manufactured artificial sky by some new 

 chemical reactions produced by light, in order to demonstrate the 

 truth of these conclusions. Another outcome from his interest in this 

 line of inquiry was his work on the putrefactive influence of the 

 floating particles of the air. This he summarised in two lectures ; 

 one on " Fermentation, and its bearings on Surgery and Medicine," 

 delivered before the " Glasgow Science Lectures Association " in 

 1876, and one on " Dust and Disease," in the course of which he 

 described a firetnan's respirator made from cotton wool and glycerine 

 which he had invented. 



More important scientifically was his valuable investigation into 

 Dr. Bastian's claims to the discovery of the spontaneous generation 

 of bacteria in vegetable infusions. As Tyndall has told us, as a 

 believer in the nebular hypothesis, he is logically bound to believe 

 that spontaneous generation did come about some time ; but with 

 true scientific candour he clearly showed that Dr. Bastian's experi- 

 ments had not been performed with sufficient care, and that when full 

 precautions are taken, the bacteria do not appear in the infusions. 



His geological work is far more important than his biological. 

 His first contribution to this subject was a lecture " On some of the 

 Eruptive Phenomena of Iceland," delivered before the Royal Institu- 

 tion in 1853, in which he illustrated by experiments the causes of 

 Geysirs. His remaining geological papers may be divided into two 

 groups, first, those bearing on slaty cleavage; and second, on glaciers 

 and glaciation. His main contribution to the former was published 

 in three papers in 1856 ; one was "Observations on the Theory of the 

 Origin of Slaty Cleavage of H. C. Sorby" {Phil. Mag., vol. xii., pp. 161- 

 164), the second was a lecture on " Crystalline and Slaty Cleavage," 

 finally published in his " Fragments of Science," and the third was a 

 "Comparative View of the Cleavage of Crystalline and Slaty Rocks " 

 {Proc. R. Inst., vol. ii., pp. 295-308). In these three papers he agreed 

 with Sorby as to the fundamental difference between the mechanical 

 and crystalline cleavage, and annihilated Professor Sedgwick's view 

 that slaty cleavage is identical with crystalline, and that therefore 

 mountains composed of slate are really often one huge crystal. 



But Tyndall went further than Sorby and showed that slaty 

 cleavage can be induced by pressure in an apparently homogeneous 



