404 PHILOSOPHICAL TRANSACTIONS. [ANNO 1783. 



application, and can now furnish out these 3 zones, with a very complete set of 

 double stars for such observations. We have the greatest reason to hope for suc- 

 cess in this attempt ; for he thinks there will be found a secular systematical 

 parallax of some considerable value ; nay possibly so short a space of time as 10 

 years may suffice to bring us acquainted with many hitherto unknown celestial 

 motions. Mr. H. here gives a long list of the double stars proper for this pur- 

 pose in each of the 3 zones; viz. in the equatorial zone, extending 10 degrees on 

 each side of the equator, about 150 stars ; the zone of the equinoctial colure, ex- 

 tending 10 degrees of a great circle on each side, will contain, as far as it is visi- 

 ble in our hemisphere, about 70 double stars ; and the zone of the solstitial co- 

 lure, of the same extent, will include about 120 double stars. And he adds a 

 zone of the ecliptic, which contains among others, a great many double stars 

 that may undergo occultations by the moon or planets. This is of the same ex- 

 tent, and includes about 120 double stars. 



It remains now only to make an application of this theory to some of the facts 

 we are already acquainted with, relating to the proper motion of the stars. 

 Astronomers have already observed what they call a proper motion in several of 

 the fixed stars, and the same may be supposed of them all. We ought therefore 

 to resolve that which is common to all the stars, which are found to have what 

 has been called a proper motion, into a single real motion of the solar system, as 

 far as that will answer the known facts ; and only to attribute to the proper mo- 

 tion of each particular star, the deviations from the general law the stars seem to 

 follow in those movements. By Dr. Maskelyne's account of the proper motion 

 of some principal stars, we find that Sirius, Castor, Procyon, Pollux, Regulus, 

 Arcturus, and a. Aquilae, appear to have respectively the following proper motions 

 in right ascension. — 0'.63; — 0".28 ; — 0".80 ; — 0".g3 ; — 0".41 ; — l /; .40 

 + 0".57 ; and two of them, Sirius and Arcturus, in declination, viz. 1".20 and 

 2 // .01, both southward. Let fig. 10, represent an equatorial zone, with the 

 above mentioned stars referred to it, according to their respective right ascensions, 

 having the solar system in its centre. Assume the direction ab from a point 

 somewhere not far from the 77th degree of right ascension to its opposite 257th 

 degree, and suppose the sun to move in that direction from s towards b ; then 

 will that one motion answer that of all the stars together : for if the supposition 

 be true, Arcturus, Regulus, Pollux, Procyon, Castor, and Sirius, should ap- 

 pear to decrease in right ascension, while « Aquilae, on the contrary, should ap- 

 pear to increase. Again, suppose the sun to ascend at the same time in the same 

 direction towards some point in the northern hemisphere, for instance, towards 

 the constellation of Hercules ; then will also the observed change of declination 

 of Sirius and Arcturus be resolved into the single motion o( the solar system. 

 But lest Mr. H. should be censured for admitting so new and capital a motion 



