'Ve7'y — Stellar Revolutions within the Galaxy. 12T 



Abt. XII. — Stellar Revolutions within the Galaxy ; bj 

 Fkank W. Yery. 



Attempts have been made to determine roughly the dimen- 

 sions of the system of stars constituting the Galaxy. By assum- 

 ing various values for the total mass of the stars and various 

 laws of stellar distribution, approximate mean velocities of 

 bodies moving under the combined attractions of the masses 

 may be deduced and compared with observation. In this way 

 a preliminary conception of the size of the galactic system may 

 be obtained, subject to the uncertainties of the assumptions 

 made. 



If we can measure the parallax of a body in one of the galac- 

 tic streams, a further check on these estimates is given. Such 

 an object we probably have in Nova Persei of 1901. All of 

 the novae have been galactic objects. We may safely assume 

 that Nova Persei lies either in the main galactic stream, or on 

 a side branch of no great length relatively to the thickness of 

 the stream. 



Consistent measures make it certain that the parallax of the 

 star is less than ()"'l. This gives a velocity of expansion for 

 the surrounding nebula which can not be much less than that 

 of light. We have no experimental evidence of any motion of 

 matter that is swifter than light, while cathode rays are known 

 to move with over half the velocity of light and to increase 

 their speed as the vacuum improves. Theory appears to 

 indicate that 300,000 km. per sec. is the limit of velocity which 

 can be produced by the transmission of electromagnetic strains 

 in the ether. Consequently, I shall assume that the nebulous 

 material has been moving, at least in the first part of its course, 

 with this speed. Applying this assumption to individual forms 

 in turn, on the supposition that the initial motion was nearly 

 radial, the maximum radii of the inner and outer nebulous 

 rings (89'' and 149''), and of an arc on the northeast side (321"), 

 observed by Perrine on March 29, 1901, 36 days from the out- 

 burst of the nova,* give : 



km. 

 Inner ring, l'' = (9'33 X 10^')^ 89 = 10-44x10% tt = 0'''014. 



Outer ring, 1" = (9-33X10'') 

 N. E. arc, 1" = (9-33x10" 



)" 

 ■321= 2-91x10", TTzrO'-OSS 



149= 6-26x10% 7r = 0"-024. 



If the largest motion is definitely assumed to have taken place 

 with the velocity of light, the speed of the material forming 

 the outer ring was presumably one-half as great, or 150,000 km. 



* Astrophysical Journal, xvi, 252, 1902. 



