BIOGRAPHICAL SKETCH 



1857 and 1859. Tyndall, assisted by his 

 friend, Dr. Thomas Archer Hirst, made 

 many measurements upon the glaciers in 

 continuation of the work of Agassiz and 

 J. D. Forbes. He discussed, in particular, 

 the question as to the conditions which 

 enable a rigid body like ice to move like 

 a river. He showed very clearly the 

 defects of former theories, proving by 

 repeated observations on the structure 

 and properties of ice the inefficacy of the 

 generally admitted plastic theory to ac- 

 count for the phenomena. Through the 

 direct application of the doctrine of 

 regelation, he arrived at a satisfactory 

 explanation of the nature of glacier 

 motion. The veined structure he as- 

 cribed to mechanical pressure, and the 

 formation of crevasses to strains and 

 pressures occurring in the body of the 

 glacier. In assigning to Rendu his 

 position in the history of glacier theories, 

 Tyndall gave offence to Professor 

 Forbes. A controversy followed, in 

 which the fairness of Tyndall's attitude 

 was fully vindicated. 



The expedition to Switzerland, under- 

 taken for a scientific purpose, had a 

 secondary outcome. Tyndall was fasci- 

 nated by the mountains, and from that 

 time forward yearly sought refreshment 

 in the Alps when his labours in London 

 were over. He became an accomplished 

 mountaineer. In company with Mr. 

 Vaughan Hawkins he made one of the 

 earliest assaults upon the Matterhorn in 

 1860. He crossed over its summit from 

 Breuil to Zermatt in 1868. The first 

 ascent of theWeisshorn was made by him, 

 in 1 86 1. Tyndall's descriptions of his 

 Alpine adventures are not only graphicand 

 characterised by his keen interest in scien- 

 tific problems, but show a poetical appre- 

 ciation of mountain beauties in which he 

 is approached by few Alpine travellers. 



The very important series of researches 

 on "Radiant Heat in its Relation to 

 Gases and Vapours," which occupied him 

 on and off for twelve years, and with 

 which his name will be always especially 

 associated, were begun in 1859. He 

 was led from the consideration of glacier 

 problems to study the part played by 

 aqueous vapour and other constituents 

 of the atmosphere in producing the 

 remarkable conditions of temperature 

 which prevail in mountainous regions. 

 The inquiry was one of exceptional diffi- 

 culty. Prior to 1859 no means had been 

 found of determining by experiment, as 

 Melloni had done for solids and liquids, 

 the absorption, radiation, and trans- 

 mission of heat by gases and vapours. 

 By the invention of new and more deli- 

 cate methods Tyndall succeeded in 

 controlling the refractory gases. He 

 found unsuspected differences to exist in 

 their respective powers of absorption. 

 While elementary gases offered practi- 

 cally no obstacle to the passage of heat 

 rays, some of the compound gases 

 absorbed more than eighty per cent, of 

 the incident radiation. Allotropic forms 

 came under the same rule ; ozone, for 

 example, being a much better absorbent 

 than oxygen. The temperature of the 

 source of heat was found to be of 

 importance : heat of a higher tempera- 

 ture was much more penetrative than 

 heat of a lower temperature. 



The power to absorb and the power to 

 radiate Tyndall showed to be perfectly 

 reciprocal. He also established that, as 

 regards their powers of absorption and 

 radiation, liquids and their vapours res- 

 pectively follow the same order. Thus 

 he was able to determine the position of 

 aqueous vapour, which, on account of 

 condensation, could not be experimented 

 upon directly. Experiments made with 



