BIOGRAPHICAL SKETCH 



dry and humid air corroborated the 

 inference that, as water transcends all 

 other liquids, so aqueous vapour is 

 powerful above all other vapours as a 

 radiator and absorber. These results, 

 questioned by Magnus and by a few 

 later experimenters, but fully established 

 by Tyndall, explained a number of 

 phenomena previously unaccounted for. 

 Since Wells's researches on dew, no fact 

 lias been established of greater impor- 

 tance to the science of meteorology than 

 the high absorptive and radiative power 

 of aqueous vapour. Many years later 

 an experiment made in his presence by 

 Mr. Graham Bell suggested to Tyndall 

 a novel and interesting method of indi- 

 rectly confirming his former results. 1 



Using a dark solution of iodine in 

 bisulphide of carbon as a ray-filter, 

 Tyndall was able approximately to 

 determine the proportion of luminous 

 to non-luminous rays in the electric and 

 other lights. He also found that the 

 obscure rays collected by means of a 

 rock-salt lens would ignite combustible 

 materials at the invisible focus ; while 

 some non-combustible bodies, exposed at 

 the same dark focus, became luminous 

 or calorescent. The astounding change 

 in the deportment of matter towards heat 

 radiated from an obscure source which 

 accompanies the act of chemical com- 

 bination, and many other points of equal 

 importance, were first established by 

 these researches, for which Tyndall 

 received the Rumford medal in 1869. 

 Nine memoirs on these subjects were 

 published in the Philosophical Transac- 

 tions, and many additional papers in 

 other journals. They have been gathered 

 together in Contributions to Molecular 



1 See "Action of Free Molecules on Radiant 

 Heat, and its Conversion thereby into Sound," 

 Pkil. Trans., 1882, pt. i. 



Physics in the Domain of Radiant Heat 

 (see p. 12). This volume also includes 

 a series of striking experiments on the 

 decomposition of vapours by light, 

 wherein the blue of the firmament and 

 the polarisation of sky-light illustrated 

 on skies artificially produced were 

 shown to be due to excessively fine 

 particles floating in our atmosphere. 



While engaged upon the last-mentioned 

 inquiry, Tyndall observed that a lumi- 

 nous beam, passing through the moteless 

 air of his experimental tube, was invisible. 

 It occurred to him that such a beam 

 might be utilised to detect the presence 

 of germs in the atmosphere : air incom- 

 petent to scatter light, through the 

 absence of all floating particles, must be 

 free from bacteria and their germs. 

 Numerous experiments showed "opti- 

 cally pure " air to be incapable of 

 developing bacterial life. In properly 

 protected vessels infusions of fish, flesh, 

 and vegetable, freely exposed after boiling 

 to air rendered moteless by subsidence, 

 and declared to be so by the invisible 

 passage of a powerful electric beam, 

 remained permanently pure and un- 

 altered ; whereas the identical liquids, 

 exposed afterwards to ordinary dust- 

 laden air, soon swarmed with bacteria. 

 Three extensive investigations into the 

 behaviour of putrefactive organisms were 

 made by Tyndall, mainly with the view 

 of removing such vagueness as still lin- 

 gered in the public mind in 1875-6, 

 regarding the once widely-received doc- 

 trine of spontaneous generation. Among 

 the new results arrived at the following 

 are noteworthy. Bacteria are killed 

 below 1 00 C. ; but their desiccated 

 germs those of the hay bacillus in par- 

 ticular may retain their vitality after 

 several hours' boiling. By a process 

 which he called " discontinuous heating." 



