1864.] 



President^ Address, 



515 



Einally, although it must be confessed that the knowledge acquired 

 of the intimate structure of the nervous centres has as yet afforded 

 but little direct insight into their functional mechanism, it cannot be 

 doubted that approved and trustworthy investigations of structure tend 

 powerfully to promote physiological truth, by enabling us to distinguish 

 between true and false anatomical data when used as a basis of physio- 

 logical reasoning, and by sweeping away the imaginary groundwork of 

 much vain speculation and erroneous doctrine. 



Me. Claeke, 



- I beg leave to present you with this Medal, which has been awarded 

 to you, on the recommendation of those in the Council most competent 

 to judge of the subjects on which you are engaged, as a well-earned 

 reward of your persevering labours, which the Council is well aware 

 have demanded from you the devotion of all the leisure remaining to 

 you amidst the duties of an active professional career. I need scarcely 

 add that the Council hopes that this mark of approbation of services 

 already performed will also be an incitement to further labours in the 

 same or in kindred fields of research. 



The Council has awarded the E-umford Medal to Professor John 

 Tyndall, F.B.S., for his researches on the Absorption and Eadiation of 

 Heat by Gases and Vapours. 



Previously to the researches of Professor Tyndall, hardly anything 

 had been done in the way of an experimental determination of the 

 absorption of radiant heat by gases and vapours. Melloni had inferred 

 from his experiments that atmospheric air is sensibly diathermanous in 

 a length such as that of an ordinary room, while Dr. Pranz came to the 

 conclusion that a column of air only 3 feet long absorbed more than 

 3^ per cent, of the heat-rays from an argand lamp. The discrepancy 

 of these results gives some view of the difficulty of the experiments ; 

 but it is only by the perusal of the earlier part of Professor Tyndall's 

 first m.emoir on the subject, that the skill and patience can be appre- 

 ciated with which the various sources of error were one by one detected 

 and eliminated by him. 



In his first memoir he shows that the elementary gases, hydrogen, 

 oxygen, nitrogen, as well as air freed from moisture and carbonic acid, 

 when examined in a length of about 4 feet, exert on the heat radiated 

 from lampblack at 212°, an absorption not exceeding about 3J per cent., 

 and liable to be altered by the slightest impurity present in the gases. 

 The results obtained with compound gases and with vapours, on the 

 other hand, were very different,' — defiant gas, for instance, in the same 

 length absorbing 81 per cent, of the incident heat. About twenty gases 

 and vapours were examined, and that not only at atmospheric pressure 

 (or, in the case of vapours, in a state of saturation), but also at a variety 



