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, 

 Qb° 16', which are the results deduced by Mr. Airy. The point determined 

 by M. Argelander is in R. A., 256° 25', and K P. D. 51° 23', resulting from 

 the examination of twenty-one stare haviog a proper motion exceeding one 

 minute per annum in arc. The velocity of the sun's motion relatively among 

 the stars, according to M. Otto IStruve, 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 approachiug that lumi- 

 naiy. 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 coiu*se will be 

 obliquely upward on the north side of this plane. Here we must consider the 

 difficulty of determining with exactness the dii'ection 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. 

 It supposes the non-recognition in those motions of any general directive 

 cause, such as, for example, a common cii'culation 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 cm-rent 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, biit 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 



