1833.] Progress of European Science. 51 
with his mural quadrant, detected a change of place in the pole-star, amounting to 
35, 40, or 45 seconds, attributed it to parallax, and regarded it as confirmatory of 
Hoox’s discovery. Indeed, the observations of Hook, as well as of those who 
preceded him, although nominally in search of parallax, had for their object little 
else than the confirmation or verification of the Copernican system ; and this arriv- 
ed at, there seems to have been but little disposition to repeat them. 
** Hence it was that the brilliant discoveries of Newron having placed the accuracy 
of the Copernican system beyond all possibility of doubt, the investigation of 
parallax was not resumed till the latter end of November, in the year 1725, at 
which time Motynevx erected his 24-feet zenith sector, by GraHaAM, in his ob- 
servatory at Kew*. ‘On the 3rd of December, y Draconis was, for the first time, 
observed as it passed near the zenith, and its situation carefully taken with the 
instrument ; and again, on the 5th, 11th, and 12th, when, no material change in 
the star’s place having been detected, further observations seemed needless, since it 
was a time of the year when no sensible alteration of parallax could soon be ex- 
pected.” Bsapury, however, being on a visit to his friend MotyNeux, was 
‘tempted by curiosity to repeat the observation on the 17th, and perceived the 
Star pass a little more southerly than when it had been observed before :’ suspect- 
ing that the apparent change of place might be owing to erroneous observation, it 
was observed again on the 20th,and he found the star still farther south than in the 
preceding observations. This sensible alteration surprised himself and MotyneEvx, 
in as much as it was the contrary way from which it would have been, had it pro- 
ceeded from an annual parallax of the star; but being incapable of accounting for 
it by want of exactness in the observations, and having no notion of any other 
cause from which such apparent motion could proceed, they suspected that some 
change in the materials of the instrument itself might have occasioned it. Under 
this apprehension, they remained some time, but being at length fully convinced, by 
repeated trials, of the great exactnesss of the instrument, and finding, by the gra- 
dual increase of the star’s distance from the pole, that there must be some regular 
cause which produced it, they examined nicely at the time of each observation how 
much it was; and about the beginning of March,1726, the star was found to be 20” 
more southerly than at the time of the first observation. It now, indeed, seemed 
to have arrived at its utmost limit southward ; for in several observations made 
about this time, no sensible difference could be detected in its situation. By the 
middle of April, it appeared to be returning towards the north, and about the be- 
ginning of June, it passed at the same distance from the zenith as it had done in 
December, when it was first observed. From the quick change in the star’s de- 
clination about this time (it increasing a secondin three days), they concluded that 
it would now proceed northward, as it before had gone southward of its present 
situation ; and it happened as was conjectured ; for it continued to move north- 
ward till September following, when it again became stationary, being then near 
20” more northerly than in June, and no less than 39” more northerly than it had 
been in March. From September, it returned towards the south, till it arrived, in 
December, at the very same situation it had been at that time twelve months, al- 
lowing for the difference of declination ‘on account of the precession of the 
equinox.’ 
“Such is a brief history of the Kew observations ; commenced, indeed, for the 
determination of sensible parallax, but which, as subsequently in the hands of Her- 
* Philosophical Transactions, vol. xxxv. p. 639. 
H 2 
