THE SUN'S MOTION IN SPACE. 167 



He points out that we may arbitrarily take as the zero of our 

 space coordinates, the place of one body or the mean of the places 

 of many bodies ; and in computing the sun's motion we are really 

 referring that motion to the mean place of the stars included in 

 the investigation, considered as a fixed point, or more strictly as a 

 point of reference. Denoting by R the sun's proper motion as 

 seen from the distance of a star of the first magnitude, Airy found 

 the elements of the solar motion for suppositions (a) and (b) to 

 be as follows, for the epoch 1840 (?): — 



(a) R.A. = 256-°9, D.= +39-°5, R. = L"269 



(b) 261-°5, + 24-°7, 1-"912 



Struve had, in his 'Bestimmung der Constante der Praecession/ 

 found only 0"339 for the quantity of the solar motion, just about 

 one sixth of Airy's estimate. This will serve to indicate the 

 uncertainty as to the velocity of translation through space, deduced 

 in this way. 



(48) Carrick, 1859} — Carrick's paper on the sun's orbit plane, 

 in the proceedings of the Literary and Philosophical Society of 

 Manchester, discussed, I believe, the solar motion. [As there is 

 no available copy in Sydney I cannot verify this however]. 



(49) Faye, 1859? — In discussing the effect of the motion of the 

 solar system through space, upon Fizeau's then recent attempt to 

 determine whether the azimuth of the polarisation of a refracted 

 ray is affected by the movement of the refracting body, 3 Faye 

 quoted the value assigned by Otto Struve and Peters for the year 

 1859, as being 



R.A. = 259-°7, D. = + 34-°5, Y. = 7-9 kilometres per second. 



(50) Liagre, 1859} — Liagre's memoir to the Brussels' Royal 

 Academy of Sciences in 1859, furnished references to the results 

 obtained by different investigators and discussed the significance 



1 Proc. Lit. Phil. Soc, Manchester, Vol. i., p. 187, 1860. 



2 Sur les experiences de M. Fizeau, considerees au point de vue du 

 mouvement de translation du systeme solaire. — Comptes rendus xlix., 

 1859, pp. 870 - 875. 3 Ibid., pp. 717 - 723. 



4 Sur les mouvements propres des etoiles et du soleil. — Brux. Bull. 

 Acad, viii., 1859, 158. 



