SPEECHES AT THE RECENT TYNDALL BANQUET. 655 



of those that we have to deal with can, such is far from being the case 

 with other gases equally transparent with regard to light. Dr. Tyndall 

 found that as a rule the more complex the composition of a gas the 

 greater is its defect of diathermancy. To confine ourselves to the two 

 gases which occur in the atmosphere mixed with its main constituents 

 I allude of course to carbonic acid and to water in the gaseous state 

 of vapor he found that both, especially the latter, which likewise is 

 present in by far the larger quantity, are very distinctly defective in 

 diathermancy, and he concluded that the main part of the absorption 

 of solar heat in passing through the atmosphere, absorption as distin- 

 guished from scattering, is due to the watery vapor which it contains. 

 From this result he drew important inferences as to atmospheric tem- 

 perature and climatological conditions. Dr. TyndalPs researches on 

 the relation of gases to radiant heat came naturally before me dur- 

 ing my long tenure of office as one of the Secretaries of the Royal 

 Society ; and for my own part I may say that it seemed to me all 

 along that the results were established on so firm a basis, and the con- 

 clusions regarding the invisible radiations were so perfectly analogous 

 to what we know to be true regarding the visible ones, where the in- 

 vestigation is comparatively easy, that the work bore on it the stamp 

 of truth. The conclusions were not, however, accepted without op- 

 position. In the late Professor Magnus, Dr. Tyndall met a foeman 

 worthy of his steel ; a foeman, however, only in the sense of an in- 

 tellectual athlete ; for socially I doubt not they were the firmest 

 friends, and their friendship was even cemented by the fact that 

 they were both alike seeking after truth in a similar subject. But 

 truth only gains by opposition : its defenders are led to engage in 

 fresh researches, which end in strengthening its foundations. I think 

 that the validity of Dr. Tyndall's results is now generally admitted. 

 If some hesitation is still felt, it arises mainly, I think, from miscon- 

 ception ; from imagining that assertions which were meant to apply 

 only to heat-rays of such refrangibilities as to be absorbed by water 

 were meant to be affirmed of the invisible radiations generally which 

 lie beyond the extreme red. The time reminds me that I must only 

 very briefly refer to another investigation in which Dr. Tyndall has 

 more recently been engaged, and of which the interest is biological, 

 while the means of investigation are physical ; I allude, of course, to 

 the question of abiogenesis. Here, again, Dr. Tyndall was working 

 on contested ground, and the objections of opponents stimulated him 

 to fresh inquiries, which resulted in the continual strengthening of his 

 negative conclusions. In the course of his work he was led, for in- 

 stance, to the discovery of the great difference which exists between 

 the germs of microscopic creatures and the creatures themselves, in 

 relation to their power of resisting the destructive influence of a high 

 temperature. This discovery not only detected a source of error in 

 some experiments which had seemed to favor the hypothesis of abio- 



