ON STELLAR AND NEBULAR DLSTANCES. 



Bv PROFESSOR IRAXK W. XERY. 



West'icood Astropliysical Observatory. Westwood, Massachusetts, U.S.A. 



(Continued from page 332.1 



Amdnc. the possible modes of origin of a galaw, 

 we have the clashing of inter[ienetrating streams of 

 matter moving in different directions. Within the 

 region of intersection kinetic energy is more or less 

 completely destroyed and converted into heat through 

 collision and friction. Equal streams of meteorites 

 moving in o[)posite directions are probabh' capable 

 of producing in this way a fixed focus of most 

 intense heat which perhaps might develop into a 

 galaxy : or if the meteoritic swarms were uneciual, 

 or met at an acute angle, a resultant motion would 

 continue in the composite aggregation. The first 

 stars should be nearh- devoid of local motion. 



The dimensions of a galaxy may result in part 

 from the size of the section of the original colliding 

 meteor streams, and partly from the intensit\' of the 

 perturbations (both astronomical and physical) which 

 are engendered by the clash. Eventually, the 

 meteoritic streams will come to an end, and the fierj- 

 rain of colliding particles will cease, making way for 

 the interaction and further evolution of intensely 

 heated bodies, born from the coalescence of the 

 interacting masses. W'e have reason to believe that 

 the Orion-tvpe stars represent some of these early 

 stages of stellar development. 



It is now known that the galactic helium stars 

 have not only small proper motions, but very small 

 linear velocities in the line of sight. If we assume 

 that the}- have developed recently from masses of 

 matter in which kinetic energy has been largely 

 annulled in the production of thermal energy, their 

 slow motion is explained. Being too far apart and 

 too uniformly distributed to acquire marked individual 

 acceleration in d-^finite directions, they may never- 

 theless continue to drift along in the residual direction 

 which is proper to the swarm. Rancken, in 1882,* 

 by considering proper motions of star-groups 

 associated with the .Milkv Way, found evidence of a 

 star-drift along the course of the stream. The 

 research requires the segregation and separate investi- 

 gation of special groups which are inextricably 

 entangled and lost by indiscriminate methods of 

 averaging. Rancken's research was confined to stars 

 within 30'^ of the galactic plane, and the drift along 

 the Milky Way appears to affect stars of the Sirian 

 type principalis- : but these stars are only a little 

 more advanced than stars of the Orion type. They 

 move a little faster thati the helium stars, and would 

 barelv show sensible proper motions at a distance of 

 one hundred light-\ears. Like the Orion stars thev 



might hi- suitable for disclosing the refiected solar 

 motion. 



In assuming an approximate diameter of one 

 hundred and twent}- light-years for the Galaxy, my 

 purpose being to institute a comparison with the 

 nebulae, it was expressh- stated that only the brighter 

 central regions were considered, for the reason that 

 the less luminous parts are unlikely to be observed 

 in verv faint nebulae. It was to be presumed that 

 the outer boundaries of the Galaxy, in its diffusely 

 scattered borders, are much more distant than sixty 

 light-years (in fact, I suggested for this outer limit a 

 distance ten times as great) ; but regarding the 

 brighter portions of the Milky Way as segments of 

 slightly eccentric arcs of spirals along which myriads 

 of stars are grouped in very much closer array than 

 in our own portion of the great aggregation, the 

 distance assigned to the nearest region of condensa- 

 tion is derived on the following suppositions : 

 (1) That the novae, as a rule, are situated in the 

 crowded spaces of the Milky Way : (2) that Nova 

 Persei (1901) was one of these typical novae ; 

 (3) that it is not possible for matter to move with a 

 greater velocity than that of light; whence it follows 

 from the most rapid expansion of some parts of the 

 nebulosity which appeared temporarily around this 

 star, that its distance and that of the associated 

 galactic stream, cannot be over sixt\' light-years. 



There have been suggestions that the expansion of 

 the nebulosity around Nova Persei may have been 

 due to the motion of gaseous molecules driven off by 

 light-pressure from the excessive intensit}- of 

 luminosit\- at the maximum outburst of light ; but 

 in this case no one supposes that the velocity can 

 have been at all comparable with that of light, and 

 it follow s that the star ought to be very near to us. 

 This hypothesis, however, cannot be maintained, 

 because measurements of the star's parallax reject 

 the supposition. Professor Newcomb is the only 

 astronomer of note who has contended that this 

 marvellous occurrence bears w itness to the existence 

 in nature of velocities, in material particles, which 

 are greater than that of light. By so doing, 

 Newcomb opposed the unanimous opinion of 

 phvsicists, basing his opposition, presumably, upon 

 an exaggerated estimate of the accuracy of 

 parallactic measures. 



One other suggestion remains : which is, that the 

 moving particles were positive ions electrically 

 discharged. These mav reach velocities of a high 



Astronoinische Nachrichleii, No. 2482. 



