An account of the Electro- Magnetic Engine. 131 



England, possessing, as she does, the most enormous capital for the 

 purposes of experiment, should remain so indifferent on a subject 

 of such vast importance. He has obtained a patent for his invention 

 throughout the kingdom of Saxony. 



Address of the President, Sir J. F. W. Herschel, Bart, on the pre- 

 sentation of the Gold Medal of the Royal Astronomical Society, to 

 Professor Bessel, at the Anniversary Meeting, February 12, 1841, 

 for his observations and researches on the Parallax of 61 Cygni. 



Gentlemen,— The Report of the Council has placed before you 

 so ample a view of the state of the Society, of its labours during 

 the last year, of the accessions to its members, and of the many 

 and severe losses it has had to deplore, that little is left for me to 

 add, except my congratulations on its continued and increasing pros- 

 perity. It would be inexpressibly gratifying to me if I could per- 

 suade myself that my own exertions in its chair had contributed, 

 even in a small degree, to that prosperity ; but, alas ! I have felt only 

 too sensibly how very feebly and inefficiently, especially during the 

 last year, owing to a variety of causes, but chiefly to residence at a 

 distance from London, I have been able to fill that most honourable 

 office. 



The immediate object of my now addressing you, Gentlemen, is to 

 declare the award by your Council of the gold medal of this Society to 

 our eminent associate, Mr. Bessel, for his researches on the annual 

 parallax of that remarkable double- star 61 Cygni, — researches which 

 it is the opinion of your Council have gone so far to establish the ex- 

 istence and to measure the quantity of a periodical fluctuation, annu- 

 al in its period and identical in its law with parallax, as to leave no 

 reasonable ground for doubt as to the reality of such fluctuation, as 

 something different from mere instrumental or observational error : 

 an inequality, in short, which, if it be not parallax, is so inseparably 

 mixed up with that effect as to leave us without any criterion by 

 which to distinguish them. Now, in such a case, parallax stands to 

 us in the nature of a vera causa, and the rules of philosophizing will 



