of the Sun and Solar Syfiem . 267 
the rules of philofophizing diredt us to refer all phenomena to 
as few and fimple principles as are lufficient to explain them. 
Thus, for inftance, we lee the ftars and planets rife and fet 
every day : now, as it is much more limple to admit the earth 
to turn once in 24 hours, than to fuppofe every {ingle fhar to 
revolve round the earth in that time, we very juftly afcribe a 
diurnal motion to the earth ; but yet, fmce we find that the 
planets do not every night exactly retain their relative places 
among the ftars, we next admit that lucli deviations from the 
law, which all the reft feem to obey, are owing to a proper 
motion of their own. To apply this to the folar fyftem. — 
Aftronomers have already obferved what they call a proper mo- 
tion in feveral of the fixed ftars, and the fame may be fup- 
pofed of them all. We ought, therefore, to refolve that 
which is common to all the ftars, which are found to have what 
has been called a proper motion, into a fugle real motion of 
the folar fyftem, as far as that will anfwer the known facts, 
and only to attribute to the proper motion of each particular 
liar the deviations from the general law the ftars feem to 
follow in thole movements. 
By Dr. maskelyne’s account of the proper motion of 
fome principal ftars*, we find that Sirius, Caftor, Procyon, 
Pollux, Regulus, Ardturus, and a Aquilae, appear to have re - 
fpedtively the following proper motions in light afeenfion. 
o ' ' 6^ ■ 
o 
// 
,28; -o",8o; — o",93 ; 
- o",4.1 
~ i",4o; 
and +o // .^*7; and two of them, Sirius and Ardturus, in de- 
clination, viz. 1 ',20 and 2", 01, both fonthward. Let fig. 3. 
reprefent an equatorial zone, with the above mentioned ftars 
referred to it, according to their refpective right afeenfions. 
* Ailronomical Obfcrvacions made at the Royal Obfcrvatory at Greenwich. 
3 having 
