89 



Inconvenience having arisen from the collection which the 

 Porter has hitherto been in the habit of making from the Fellows 

 of gratuities for the delivery of the Lists of the Society, the Council 

 have now ordered that from the day of the next anniversary, he 

 shall receive, in lieu of such gratuities, and of his former salary, a 

 salary at the rate of £60 per annum. 



The Copley Medal has been adjudged to Professor Airy of Cam- 

 bridge, for his papers on the construction of the Achromatic Eye- 

 pieces of Telescopes, and on the Achromatism of Microscopes ; on 

 the Spherical Aberration of Eye-pieces, and for his other papers on 

 optical subjects in the Cambridge Philosophical Transactions. 



The rules for the practical construction of eye-pieces, which were 

 chiefly formed by the elder Dollonds, were probably deduced by re- 

 peated trials, conducted with the usual skill and sagacity of those 

 great opticians, rather than by any very accurate reference to their 

 mathematical theory : in whatever manner, however, they were dis- 

 covered, they have continued to be adopted by opticians with very 

 little alteration since that time. 



The correction of the spherical and chromatic aberration of eye- 

 pieces is at least as important in practice as those of object-glasses; 

 and whilst the theory of the latter has been more than once subjected 

 to a complete analysis, that of the former has been almost altogether 

 neglected. The elaborate and complicated formulae of Euler are 

 altogether useless for the present constructions ; and the more prac- 

 tical investigations of Boscovich, though opening the way to more 

 accurate results, have failed to satisfy the required conditions. Pro- 

 fessor Airy, by a more accurate analysis of the theory of oblique pen- 

 cils of rays, and by connecting his investigations more strictly with 

 the practical conditions of the problem to be solved, has been enabled 

 not merely to satisfy the common constructions and the rules for 

 effecting them, butlikewise to point out other constructions with their 

 corresponding rules ; and though such constructions have been found, 

 upon trial, to be at least not superior to those which are already in 

 use, it must always be considered as an important step in the ad- 

 vancement of science, that theory should be at least coextensive with 

 practice., and should become a leader and a guide to the latter, instead 

 of a follower in its train. But though the Council have selected the 

 papers on the theory of the correction of the chromatic and spherical 

 aberration of eye-pieces, as forming the principal ground of their de- 

 cision, yet they are anxious to combine with them other papers in the 

 same Transactions, as deserving of particular commendation, and as 

 showing the profound acquaintance of their author with every branch 

 of optical science. Amongst these maybe mentioned the paper on 

 the Double Refraction of Quartz, which is of very recent publication, 

 inasmuch as it affords one of the most striking a posteriori proofs 

 which have hitherto been discovered of the truth of the undulatory 

 theory of light; a most difficult mathematical investigation, essentially 

 founded upon that theory, leads him to expect the appearance of phe- 

 nomena of great beauty and intricacy, as the result of certain experi- 



