1887.] 



President's A ddress. 



189 



electrodes formed of a given substance, an analysis of the spark 

 reveals a usually complicated spectrum of bright lines, characteristic 

 of the chemical substances present. The arrangement of the lines in 

 most cases seems capricious, while in other instances we have repeti- 

 tions of lines, or else rhythmical flutings, indicative of law, though 

 one of no simple character. There can be no reasonable doubt that the 

 periodic times indicated by the bright lines seen in the spectrum are 

 those belonging to the component vibrations of the chemical mole- 

 cules themselves ; and the appearance is just such as would be pro- 

 duced by a tolerably complex dynamical system vibrating under the 

 action of internal forces of restitution. Xow such a system may 

 really be composed of two or more simpler systems, held together 

 less firmly than the parts of one of the simpler systems ; and the 

 complex vibrations of the whole may be made up of those of 

 the several simpler systems, modified, however, by their mutual 

 connexion, together it may be with others due to the mutual con- 

 nexion of the simpler systems regarded each as a whole. It is con- 

 ceivable that relations of chemical composition may thus be pointed 

 out even between substances which we deem elementary, and which 

 from their great stability we may, perhaps, never be able actually to 

 decompose. 



But I must apologise for having taken up your time with specula- 

 tions as to the future ; I will turn now to some mention of the action 

 of your Council during the past year, and of the progress made by 

 committees appointed by the Council. 



In response to an invitation received from the Academy of Sciences 

 of Paris, that the Society should be represented at the International 

 Conferf nee of Astronomers, which it was proposed should assemble in 

 Paris, m the spring, for the purpose of deliberating about concerted 

 action for obtaining a complete map of the starry heavens by means 

 of photography, your Council requested the Astronomer Royal to 

 represent the Society on that occasion. The conference met, as it 

 was proposed, last spring, and I believe that the English astrono- 

 mers at least think that a good foundation has been laid for concerted 

 action in that great undertaking. 



As the Fellows are already aware from a circular which has been 

 issued, the Council have decided to make a change in the mode of 

 publication of the ' Philosophical Transactions.' The average yearly 

 volume is a good deal more bulky now than it was at the beginning 

 of the century, and its size is such as not unfrequently to make it 

 desirable to bind one volume in two. The sciences, moreover, which 

 are represented in the ' Philosophical Transactions,' divide them- 

 selves very naturally into two groups : mathematics, physics, and 

 chemistry forming one, and the biological sciences the other. The 

 Council have decided to issue the ' Transactions ' from henceforth in 



