ae 
LOMO LOLA: 
DETERMINATION OF CONSTANT OF NUTATION. 127 
ber. 
rae 
Notice of the Determination of the Constant of Nutation by 
the Greenwich Observations, made as commanded by the 
British Association. By the Rev. T. R. Rozinson, D.D. 
Ir is now a century since Bradley, by his brilliant discoveries 
of the aberration of light, and the nutation of the earth’s axis, 
became the founder of accurate astronomy. By them he not 
merely explained the seemingly anomalous movements which, 
though noticed by others before him, were first established by 
his observations on authoritative evidence, but he also demon- 
strated that a degree of precision, which the other astronomers of 
that time could scarcely conceive, was perfectly attainable. From 
the commencement of his career to the present day the impulse 
thus given has never failed, and each successive year has brought 
improvements to the construction of astronomical instruments, 
to the methods of observing, or, what is equally important, to the 
reductions by which these observations are made available to 
science. 
Yet it must be acknowledged that in respect of both aberra- 
tion and nutation nothing was added to the researches of Brad- 
ley till within a few years, when Struve, Brinkley, and Richard- 
son resumed the inquiry as to the first, and contracted within 
very narrow measures the limits of its uncertainty. The second, 
of these astronomers also investigated the constant of nutation, 
and his result is generally adopted by British astronomers. In 
Germany, however, the authority of M. Besselhas given currency 
to a different value of this important element, deduced by 
Von Lindenau, and though the two differ only + of a second, 
(7760.000 “66 AGG of the telescope used in observing,) such is the accu- 
? ? 
racy now required that even this evanescent discordance is felt 
asa disgrace toastronomy. ‘This stigma I trust is now removed 
by the work which the powerful aid of the Association has en- 
abled me to perform, and of which it is my present object to give 
a brief notice to this section, the fuller details requiring a dif- 
ferent mode of publication. 
When an observer directs the telescope of his circle to a star, 
the distance from the pole or the zenith which he obtains is but 
crude ore, and much labour is required to obtain its precious 
contents. The refraction of the atmosphere prevents us from 
seeing it in its true place ; its effect must be computed and cor- 
rected ; the light by which we see it takes time to travel through 
