52 Progress of European Science. [Jan. 
SCHEL, led to a very different result. In reading it, we are at a loss whether most 
to admire the mode in which the observations were conducted, or the modest un- 
assuming manner in which they are recorded : no possible source of error is allow- 
ed to pass without the most rigid examination—no theory suffered to embarrass 
the observers in their observations ; the slightest anomaly became the subject of 
suspicion, till in presumed anomaly was found the most perfect regularity. 
“That observations so conducted, leading to results so unexpected,could be aban- 
doned till the law which governed them should be unfolded, was impossible. But 
Braptey rejected all inquiries into the cause till the effects were accurately deter- 
mined; and feeling that the apparent motion was obtained by observations only of 
one year—by one instrument—and by one star,—he erected at Wanstead, aided by 
his friend GRawAmM, on the 19th of August, 1727, his zenith sector of 12% feet 
focus, formed, indeed, upon the same general plan of MoLyNEvx’s, but furnished 
with a divided arc of 6% degrees on each side of the zenith point, for the purpose 
of enabling him to ascertain, by direct observation, whether other stars than y 
Draconis would he similarly affected. The instrument’s situation, when adjusted, 
‘might be securely depended upon to half a second,’ and its telescope could be 
directed to ‘not less than 12 stars, bright enough to be seen in the day-time,’ 
throughout the year: the same changes were observed as had been previously de- 
tected with MotyNervx’s instrument. Inflexible, however, in his resolution not 
to generalise till sufficient means were collected to lead him to a ‘ probably just 
conclusion,’ the year of probation was suffered to be completed before ‘ the ob- 
servations were examined and compared :’ ¢hen it was that he satisfied himself of 
the general laws of the phenomena, and ¢hen, and not fill then, did he endeavour 
to find out their cause. Convinced that the apparent motion of the stars which 
he had observed was not owing to nutation—persuaded, that a change in the 
direction of the plumb-line with which the instrument was rectified was insuffici- 
ent to have occasioned it—and having appealed unsuccessfully to refraction,—he 
perceived, ‘ that if light was propagated in time, the apparent place of a fixed object 
would not be the same when the eye is at rest, as when it is moving’ in any other 
direction than that of the line passing through the eye and the object; and that 
when the eye is moving in different directions, the apparent place of the object 
would be different.’ He therefore announced his discovery in these words : ‘ That 
all the phenomena proceeded from the progressive motion of light and the earth’s 
annual motion in its orbit,’ or, as he afterwards called it, aberration of light. 
“But he who determined its existence determined also its constant, and fixed it 
at 20’; giving us, therefore, the interval of time in which light travels from the 
sun to the earth, as eight minutes and seven seconds, differing from that deduced 
by Roemer nearly three minutes of time, a circumstance not at all to the disere- 
dit of RoumMER, considering the imperfect knowledge of the theory of Jupiter’s 
satellites at the time he made his important discovery. 
“The observations, however, which led BRapLEy to the discovery of aberration, 
and to the determination of its constant, being as yet unpublished, have given rise 
to insinuations certainly ungenerous, and probably unjust. Impelled by more ho- 
nourable feelings, our illustrious associate BrssEx, alluding to the observations of 
+ Draconis made by BRADLEY when the sector was removed to Greenwich, says*, 
‘ Ceterum BRADELII observationes Wansteadiane liberari possunt a sectoris mu- 
tabilitate, quum se@pius, eodem tempore, observate sint stelle, in quibus aberrationt 
* Fundamenta Astronomiz, p. 124. 
