OF ARTS AND SCIENCES : NOVEMBER 8, 1865. 37 



Five liaudred and fifty-se-renth Meeting. 



November 8, 1865. — Statute Meeting. ' 



The President in the chair. 



Mr. Safford presented the following paper : — 



On the Right-Ascensions observed at Harvard College Ob- 

 servatory in the Years 1862 - 1865. By T. H. Safford. 



It is part of every astronomer's duty to assure himself in some way 

 of the accuracy of the elements upon which the reduction of his obser- 

 vations depend. If he is a meridian observer, he must make sure that 

 the right-ascensions of the clock- and polar-stars which he employs are 

 correct ; and the most thorough means of so doing is to determine 

 them by his own observations. 



It is true that this process requires much time and patience ; that 

 we, in America, are tempted to think that it has all been so excellently 

 done abroad, that anything we can do will not add to the accuracy of 

 the determinations we derive from foreign sources. I think this notion 

 is somewhat ill-founded. The quantities in question are, as above 

 stated, the right-ascensions of standard stars ; they must be predicted, 

 and are so predicted for many years in advance ; and the simple for- 

 mula by which this prediction has to be made, 



^ t — f ^ / I r 2 



= a — a" + A » -^ i_A_ 1, 



shows that not only do the errors of the modern observations come in 

 with more than their full amount, but are somewhat increased by a 

 part of those of the ancient ones. 



It ought also to be considered that the observations made with any 

 meridian instrument are liable to errors of obscure origin, which make 

 it somewhat better to use its own results to reduce other observations 

 obtained with it ; and that, on the other hand, each good instrument 

 well used, and each well-trained observer, contributes something; to the 

 general foundations of the science which no other observer or instru- 

 ment can do. 



The eminent German, EngHsh, Russian, and French astronomers 

 have followed this plan within the present century. 



