TEMSACTIONS OF THE SECTIONS. 



Section A.— MATHEMATICAL AND PHYSICAL SCIENCE. 



Pkesidext of the Section — Professor W. Gkylls Adams, M.A., F.R.S., 



F.G.S., F.C.P.S. 



THURSDAY, AUGUST 26. 



The President delivered the following Address : — 



It has been said by a former President of this Section of the British Association 

 that the President of a Section ought to occupy your time, not by speaking of 

 himself or his own feelings, but by a re\-iew 'more or less extensive of those 

 branches of science which form the proper business of this section.' He may give a 

 rapid sketch of the progress of mathematical science during the year, or he may 

 select some one special subject, or he may take a middle course, neither so extensive 

 as the first nor so limited as the second. 



There are many branches of science which have always been regarded as pro- 

 perly belonguig to our Section, and the range is already wide ; but it is becoming 

 more and more true every day that the sciences which are dealt with in other 

 sections of the Association are becoming branches of Physics, i.e. are yielding results 

 of vast importance when the methods and established principles of Physics are 

 applied to them. I wish to direct your attention to investigations which are l)eing 

 made in that fertile region for discovery, the ' border land ' between chemistry and 

 physics, where we ha'se to deal \\ath the constitution of bodies, and where we are 

 tempted to speculate on the existence of matter and on the nature of the forces by 

 which the difiereut parts of it are boimd together or become so transformed that 

 all resemblance to their former state is lost. It is not long since the theory of 

 exchanges became thoroughly recognised in the domain of Radiant Heat, and 

 yet so rapid is the progress of science that it is already recognised and accepted 

 in the theory of Chemical combination. Just as the molecules of a body which 

 remains at a constant temperature are continuously giving up their heat-motion to 

 surroimdmg molecules, and getting back from them as much motion of the same 

 kind in return, so in a chemical compound which does not appear to be undergoing 

 change, the combmiug molecules are continuously giving up their chemical or com- 

 bining motions to surrounding molecules, and receiving again from them as much 

 combming motion in return. We may say that each molecule is, as far as we can 

 see, constantly dancing in perfect time with a partner, and yet is continuously 

 changing partners. When such an idea of chemical motion is accepted, we can 

 the more easily imderstand that chemical combination means the alteration of 

 chemical motion, which arises from the uitroduction of a new element into the space 

 already occupied, and the consequent change in the motion of the new compound as 

 revealed to us in the spectroscope. We can also the more readily understand that 

 in changmg from the old to the new form or rate of motion, there may be a deve- 

 lopment of energy in the shape of heat-motion which may escape or become dis- 

 sipated wherever a means of escape presents itself We know from the experiments 

 of Dr. Joule and of M. Favre that as much heat is absorbed during the decomposi- 

 tion of an electrolyte as is given out again by the combination of the substances 

 composing it. 



