xliv Appendix. 
stellar and resisting medium. From the investigations of astronomers and 
mathematicians, conducted in a variety of ways, there cannot remain a shadow 
of a doubt of the reality of solar motion, or as to its direction in space to a 
point near to Right Ascension, 261° 29’; and to North Polar Declination, 
65° 16’, which are the results deduced by Mr. Airy. The point determined 
by M. Argelander is in R. A., 256° 25’, and N. P. D. 51° 23’, resulting from 
the examination of twenty-one stars having a proper motion exceeding one 
minute per annum in are. The velocity of the sun’s motion relatively among 
the stars, according to M. Otto Struve, is 422,000 miles, or nearly its own 
semi-diameter per diem. 
With a velocity approaching to this, it is not difficult to conceive the 
effect it must have on the solar atmosphere, if the existence of a resisting 
medium can be demonstrated. Perhaps the best proof of such a medium is 
in the observation of comets. They are known to be bodies of extreme 
tenuity, and Encke’s comet has a period of revolution round the sun which is 
continually diminishing, proving that it is gradually approaching that lumi- 
nary. The- solution proposed by Encke, and the one generally adopted, is 
that it is retarded by a very rare ethereal medium pervading the regions in 
which it moves. 
In the diagram, the direction of the sun’s motion, as projected on the 
plane of the ecliptic, is shown as Right Ascension 261° 29’, but the 
North Polar Declination of its motion being 65° 16’, its course will be 
obliquely upward on the north side of this plane. Here we must consider the 
difficulty of determining with exactness the direction of the solar motion. 
Sir John Herschel remarks, “The whole of the reasoning upon which the 
determination of the solar motion in space rests, is based upon the entire 
exclusion of any law either derived from observation or assumed in theory, 
affecting the amount and direction of real motions both of the sun and stars. 
Tt supposes the non-recognition in those motions of any general directive 
cause, such as, for example, a common circulation of all about a common 
centre 
I might thus illustrate the case. During a calm at sea the smoke from an 
ocean steamer would give the exact direction of its motion, both when the 
water was motionless, and also if it was influenced by an ocean current. A 
ship might be steaming in a northerly direction, and a current might be 
moving westerly ; if both velocities were the same, then the true motion of 
the vessel would be north-west, as also manifested from the line of smoke ; 
and a person in the ship taking observations on other ships also moving in the 
Same current, but otherwise stationary, would conclude that his ship was 
moving due north, but in reality the line of smoke would give the resultant of 
all the compounded motions affecting the vessel. Similarly we may be unable 
ll 
