i6 NATURAL SCIENCE. Jan.. 



body, whereas in the experiments of the latter some flaky particles 

 such as mica were always mixed with the substance used. Later 

 on, however, T5'-ndall recognised that the lateral yielding of the clay 

 under pressure, and the consequent tangential sliding of one particle 

 over another, contributed very largely to the result. 



Tyndall's glacier work was more extensive and important. His 

 main contribution was the discovery of regelation, by which the 

 method of glacier motion is easily intelligible. He next showed, by 

 some difficult work on the Mer de Glace in mid-winter, that the 

 glaciers move in the winter as well as in the summer, and determined 

 the rate. He subsequently showed how the well-known " veined 

 structure " of glaciers is a result of the flow of the ice. His principal 

 paper upon the subject was one contributed to the Philosophical 

 Transactions in conjunction with Professor Huxley in 1857. 



His studies upon this subject were collected and summarised in 

 his books on the " Glaciers of the Alps," and in " The Forms of 

 Water," which were pubKshed in i860 and 1872 respectively. In 

 addition to his work on the properties of glacier ice, he closely 

 watched the action of the glaciers and held somewhat extreme views 

 as to the extent of their erosive power. Thus he assigned a far 

 larger influence to glacial erosion in the configuration of the Alps, in 

 his lecture in 1864, than is fashionable at the present day. He 

 joined in the controversy on the origin of the Parallel Roads of 

 Glen Roy, and advocated and restated with great clearness Jamieson's 

 theory of their formation by the action of a glacier dam. 



It is, however, less on his work as an original discoverer than in 

 his brilliant powers of lucid exposition that Tyndall's influence has 

 depended. It is generally argued that lecturing was his forte, and in 

 this he was unusually successful. Most of his text-books were based 

 on his lectures, such as his " Lessons in Electricity," which were given 

 as a course of lectures to children at the Royal Institution, and show 

 his capacity for using the simplest of apparatus. His books on 

 " Sound," "Light," and "Heat, considered as a mode of Motion " were 

 also com.piled from lectures. The two first were given in a tour in 

 the United States in 1872, the profits of which, amounting to 

 13,000 dols., he presented to the Universities of Harvard, Columbia, 

 and Pennsylvania, for the endowment of research scholarships. 



The department of this work for which, perhaps, the younger 

 generation owes Tyndall the deepest debt 01 gratitude, is that, in 

 conjunction with his two friends, Herbert Spencer and Huxley, he 

 fought the fight which gained for Natural Science a free hand in the 

 investigation of the whole range of natural phenomena. This now 

 sounds like a truism ; but it was not when he wrote that " the im- 

 pregnable position of science may be described in a few words. We 

 claim, and we shall wrest from theology, the entire domain of cosnio- 

 logical theory. All schemes and systems which thus infringe upon 

 the domain of Science, must, in so far as they do this, submit to its 



