1833.] Progress of European Science. 53 
contraria fuerunt signa: qud de cansd et propter observationum prestantiam, opta- 
bile esset reperire ipsa BRADLELI autographa.’ It will, therefore, be highly grate- 
ful to him, and to astronomers in general, to be informed from this chair, that the 
manuscripts of the Wanstead observations are found !—that to the honour of the 
University of Oxford, twenty-three sheets of them are already printed ; and that 
the volume will be presented to the public with as little delay as possible, under 
the superintendence of Professor Ricaup. 
** Till within these few years,the constant, as determined by BRADLEY, was uni- 
versally employed in all our astronomical reductions ; recently, however, astrono- 
mers have re-investigated it. DrLamBre, from the eclipses of Jupiter’s satellites 
regards it 20”,25. BussEL, from BRapLEy’s Observations made at the Royal Ob- 
servatory, after he was appointed Astronomer Royal, has deduced for the con- 
stant 20,68. Linpenavu, by comparisons of Brav.Ley’s, MASKELYNE’s, 
BesseEx’s, and Ponp’s observations of Polaris, has obtained for it 20”,61. Brinx- 
LEY, from his own observations, considers it as 20”,37. Whilst Srruve, by his 
observations, draws almost the same inference, namely 20,35. 
‘* Such were the results most entitled to our confidence, when Mr. RicHarpson, 
in the hours allotted to him for repose or recreation, undertook those labours 
which form the subject of our present consideration, and of which the following is 
a brief outline. A second mural circle by Jones, after the model of that of 
TRovuGHTON’s, having been erected at the Royal Observatory, in the April of 1825, 
corresponding observations with the two instruments were carried on simultaneous- 
ly ; they were confined, indeed to a few stars, but every precaution to render them 
as accurate as possible was adopted. Thus, the index error of each instrument was 
ascertained by observing the same star alternately, by direct vision and reflection ; 
each pair, therefore, giving to its respective instrument one horizontal point per- 
fectly independent of astronomical tables, the final accuracy of the determination of 
the index error being directly as the number of pairs observed. Throughout the 
observations, the place of each star was arrived at by reference to the six micros- 
copes of each circle ; care also being taken to equalise, as nearly as possible, the tem:- 
perature of the observatory with that of the external air, so that errors to any ex-, 
tent, arising from partial expansions or erroneous divisions of the instrument, were 
effectually excluded. 
“From such unexceptionable data, fourteen stars were selected by Mr. Ricuarp- 
SON as the fittest for his purpose, being those the least affected by refraction, and the 
most affected by aberration, so that the errors of observation might have the mi- 
nimum influence upon the results, Upwards of 4000 observations he separately 
discussed, and in no instance was the actual aberration of each observed star less 
than 14” ; and the conclusion to which he has arrived is, from TrRouGuHTon’s cir- 
cle, that the Constant of Aberration is 20,505 ; whilst by Jongs’s, it is 20,502; 
the one differing from the other but three-thousandths of a second. 
“ Hook, in searching for parallax, was misled by his instrument. BranpLry, in 
detecting it was unsuccessful, but discovered aberration. Hook’s instrument was 
the work of his own hands ; BRapLEy’s was the work of Grauam. Sensible that 
much of his astronomical glory was referable to the accuracy of his instrument, 
the amateur astronomer of Wanstead was ever ready to acknowledge it ; and when 
we consider that one hundred years’ improvement in astronomical manipulations 
can alter the constant of aberration as determined by him but one half second, we 
are almost led to exclaim ‘ guando ullum inveniemus parem. ?’ 
