[ o 
accurate Obfcrvations, that, till fuch were made, it 
advanced but (lowly : For the firft con fide rable Im- 
provements that it received, in point of Theory, were 
owing to the renowned Tycho Brakes who far ex- 
ceeding thofc that had gone before him, in the 
Ex act ne fs of his Obfervations, enabled the fagacious 
Kepler to find out fomc of the principal Laws, re- 
lating to the Morion of the heavenly Bodies. The 
Invention of Telefcopes and Pendulum-Clocks af- 
fording proper Means of ftill farther improving the 
j Praxis of Aftronomy ; and thefe being alio foon fuc* 
ceeded by the wonderful Difcoveries made by our 
Great Newton, as to its Theory ; the Science, in 
both refpeds; had acquired fuch extraordinary Ad- 
vancement, that future Ages feemed to have little 
room left, for making any great Improvements. But, 
in fad, we find the Cafe to be very different $ for, 
as we advance in the means of making more nice 
Inquiries, new Points generally offer themfelves, 
that demand our Attention. The Subjed of my 
prefent Letter to your Lordfhip, is a Proof of the 
Truth of this Remark : for, as foon as I had difeo- 
vered the Caufe, and fettled the Laws of the Aber- 
rations of the fixed Stars, arifing from the Motion 
of Light, &c. whereof I gave an Account in N°. 
406. of the Bhilofophical TranfaBions ; my Atten- 
tion was again excited by another new Bhanomenon, 
viz. an annual Change of Declination in fome of 
the fixed Stars; which appeared to be toxNchy greater 
about that time, than a Preceflion of the Equinodial 
Points of *yo n in a Year would have occafioned. 
The Quantity of the Difference, tho J fmall in itfelf, 
was 
