Mr. R. A. Proctor on certain Drifting Motions of the Stars. 381 



1869. August 15. 

 The night was very clear, and the air steady, but completely saturated 

 with moisture, at a temperature of about 52°. The mean of fourteen 

 observations of the difference of reading for a Lyrse on a and j3 gave 

 only 1 1 divisions. I have no doubt that the small effect here obtained 

 was due principally to the amount of moisture in the air. 



1869. August 25. 



Observations of a Lyrse. Night fine. 



Mean value of the difference from nine observations was 

 = 33 div. 

 = 669 div. 

 c=24 inches; 

 .*. heating-power of a Lyrse = 0°* 0088 F. 



This result is again so much smaller than those obtained from Arc- 

 turus, although the observations of Arcturus were made under more 

 unfavourable circumstances with respect to altitude, that I cannot but 

 regard it as a fact that the star Arcturus does give us more heat than 

 a Lyrse, — a result probably due to the same cause which gives rise to 

 the difference in colour between these stars, viz. the greater absorption 

 of the red end of the spectrum in the case of a Lyrse than in the case 

 of Arcturus. 



I may here mention that on June 25, 1869, I made a direct com- 

 parison between Arcturus and a Lyrse. The result gave for the heat 

 received from Arcturus : that from a Lyrse : : 3 : 2 ; but on account 

 of the observations of a Lyrse having been interrupted by cloud, they 

 were not sufficiently numerous to eliminate mere errors of reading. 



From the whole of these observations I think we may conclude : — 

 that Arcturus gives to us considerably more heat than a Lyrse ; that 

 the amount of heat received is diminished very rapidly as the amount 

 of moisture in the air increases ; that nearly the whole heat is in- 

 tercepted by the slightest cloud; that, as first approximations, the 

 heat from Arcturus at an altitude of 25°, at Greenwich, is about equal 

 to that from a three-inch cube containing boiling water at a distance 

 of 400 yards. 



The heat from a Lyrse at an altitude of 60° is about equal to that 

 from the same cube at a distance of about 600 yards. The form given 

 to the pile appears likely to be useful in many inquiries respecting dif- 

 ferences of heating-power. 



Jan. 20.— Dr. William A. Miller, Treas. and V.P., in the Chair. 



The following communication was read : — 



" Preliminary Paper on certain Drifting Motions of the Stars." 

 By Richard A. Proctor, B.A., F.R.A.S. 



A careful examination of the proper motions of all the fixed stars 

 in the catalogues published by Messrs. Main and Stone (Memoirs of 

 the Royal Astronomical Society, vols, xxviii. and xxxiii.) has led me 

 to a somewhat interesting result. I find that in parts of the heavens 

 the stars exhibit a well-marked tendency to drift in a definite direction. 

 In the catalogues of proper motions, owing to the way in which the 



