140 



A paper was also read, entitled " An Account of the Construction 

 of a fluid refracting Telescope of eight inches aperture and eight feet 

 nine inches in length, made for the Royal Society by George Dollond, 

 Esq. F.R.S." By Peter Barlow, Esq. F.R.S. 



The author has, in former papers read to this Society, pointed out 

 the great variety of cases included under the general formulae relating 

 to the operation of fluid refracting telescopes, and stated the difficulty 

 of selecting, independently of experiment, the particular case which 

 was likely to produce the best result. This subject is pursued in the 

 present paper ; and the principles and calculations stated at length 

 which the author has applied in the construction of the telescope 

 which the Council of the Royal Society directed should be made by 

 Mr. Dollond, under the superintendence of the author, in order to 

 put these principles to the test of experiment, and to decide the ques- 

 tion of the expediency of proceeding in the construction of a similar 

 telescope of much larger dimensions. When the experimental tele- 

 scope was completed, it was found that its performance agreed in every 

 respect with the computed results, as well in focal distance as in 

 chromatic and spherical aberration. The arrangement of the lenses 

 was such, that the corrections are all of them made in the transmis- 

 sion of the light through the fluid, and by the fluid only. The author 

 abstains from offering any remarks on the performance of this tele- 

 scope, leaving it to those whom the Council of the Royal Society 

 may appoint, to decide upon its merits. He concludes by expressing 

 his obligations to Mr. Dollond, for the readiness with which he com- 

 plied with all the suggestions of the author, and for the accuracy 

 with which he has executed every part of the instrument. 



Anniversary Meeting, Nov. 30th. 



HIS ROYAL HIGHNESS THE DUKE OF SUSSEX, K.G., 



President, in the Chair. 



The President delivered the following Address : 

 Gentlemen, 



This is the Second Anniversary of my election to the Chair of 

 the Royal Society, and I gladly avail myself of the opportunity which 

 it affords me of renewing the expression of my gratitude to you for 

 the distinguished honour conferred upon me in electing me to it, and 

 still more for the continued kindness and support which I have re- 

 ceived from you in the execution of the duties of my office. I can 

 only assure you, Gentlemen, that if it be your pleasure that I should 

 continue to fill this Chair, I shall feel an additional motive to induce 

 me to devote my most earnest attention to the promotion of the in- 

 terests of the Society, in the perfect reliance which I place upon 

 your cooperation and assistance, and in the confident expectation 

 which I entertain, that in case I should fail in the due and efficient 

 discharge of any of my duties, I shall experience from you the most 

 kind and liberal interpretation of ray motives and conduct. 



In making my acknowledgments to the Fellows of the Society at 



