Mi Royal Astronoinical Societyl 



it h accuracy; comprising under this word the two different stfeps, 

 of exactness in making observations, and certainty in transmitting 

 them to the reader. And upon the importance of this accuracy, as 

 contrasted with number or variety, I cannot express my opinion with' 

 sufficient strength. It is matter of history that the establishment of 

 the laws of Kepler, of the system of Copernicus, and finally, of the 

 theory of gravitation, depended upon a discordance between the 

 theory of that period and the observations amounting to eight 

 minutes of arc. This was then a small quantity but certainly ap- 

 preciable, if the best instruments and best methods of the time were 

 used. Now, gentlemen, am I wrong in saying that the establish- 

 ment of a cosmical theory, infinitely more comprehensive and more 

 important than that of gravitation, may depend upon the certainty 

 of a measure to the tenth part of a second } I say, that it is more 

 than possible ; that it is highly probable ; and that there is fair pro- 

 bability of its occurring within our time. Kepler on a similar occa- 

 sion put to himself the question, " Is it likely that an observer so 

 accurate as Tycho can have been in error by eight minutes.''" and 

 boldly answered to himself, "It is impossible, and, therefore, a new 

 theory must be formed." When the question shall be put regarding 

 the measures of the Bedford Catalogue, made at a critical time, and 

 on which a future theory may hinge. Can these numbers be trusted 

 with certainty to one or two- tenths of a second ? shall we be able to 

 answer. Without doubt they can "i This leads me to a very import- 

 ant part of my present remarks. 



The Catalogue of the Celestial Cycle, as exhibited to the public, 

 contains simply the result for each star of all the observations made 

 on that star. In some cases results are given for more than one 

 epoch ; but in all cases, every result is given without exhibition of 

 the individual observations from which it was deduced. This form 

 of publication is open to a very grave objection, and one which was 

 seriously discussed by your Council. In a remark above I spoke of 

 the accuracy of published obser^j^tions as depending on two circum- 

 stances ; exactness in making the obsei'vations, and certainty in 

 transmitting them to the reader. With regard to the exactness of 

 the observations, we had the evidence of a member of the Council 

 who had compared unpublished observations made under the most 

 unquestionably favourable circumstances with individual observa- 

 tions made by Captain Smyth ; and we had also the indirect evidence 

 derived from the progressive changes in the relative positions of 

 some of the stars. These kinds of evidence probably had their weight 

 with members of the Council ; but to me, I must aver, they were 

 entirely unnecessary. My confidence in the exactness of the obser- 

 vations is purely personal. Knowing the attention which has been 

 given to the adjustments, the intentness of the observer upon his 

 work, the nerve which is made steady rather than disturbed by the 

 anxiety to procure a good observation, and the general skill in the 

 management of the instruments, I can truly say, that if an accurate 

 observation were required, I would desire that it should be made by 

 Captain Smyth. Yet I could wish that I had the means of exhibit- 



