( 134 ) 



region) is to be found. And indeed we find in table VII fig. 2 tlie 

 best marked maxima of the nebulaecurves at about 105" gal. longi- 

 tude at less than 90 degs. from the Cygnus region and a less strongly 

 pronounced one in the northern hemisphere at 280^. 



The available material is certainly not sufficient for us to decide 

 with any probability whether the secondary maxima (at 165" etc.) 

 of the curves of the tables VII and VIII i-esult indeed from the 

 arrangement of the galactic agglomerations or wliefher they are 

 produced by a merely local accumulation of nel )u lac. Among such 

 "local deviations" from the uniform distribution we ought then also 

 to reckon the Nubeculae, which apparently have such a great in- 

 fluence on the distribution of the nebulae in the soutliei-n galactic 

 hemisphere. It siiould be borne in mind that the Nubeculae are not 

 connected by streams of nebulae with the southern Milky Way and 

 neither probably by streams of stars. Nor is the influence of the 

 vast nest of nebulae, which constitutes the Nul)ecula Maior percep- 

 tible in table VIII. 



Finally, if the nebulae in the very distant regions of the system 

 remain in general invisible and hence are not included in the statis- 

 tical data given here, while they can be more easily photographed, 

 this would in connection with our preceding remarks exi)lain the 

 fact observed by Max Wolf {Sltzungsher. M'dnchenX.\X\,\l, \^.12Q) 

 that tlie mass of the very faint nebulae photographed by him are 

 scattered more uniformly over the sky than those observed visually. 



Physics. — ''Dispersion bands in absorption spectra.'' By Prof. 

 W. H. Julius. 



(Communicated in the meeting of May 28, 1904). 



The appearance of absorption lines depends on various circum- 

 stances. As to the absorption phenomena in gases and vapours, such 

 conditions as temperature, density, pressure, velocity in the line of 

 sight, intensity and direction of magnetic field, have been fully 

 studied and discussed. In the present paper we purpose to show 

 that anomalous dispersion in the absorbing gas is also, to a great 

 extent, accountable for certain typical features of the dark lines. 



An originally parallel beam of light, when passing through a 

 mass of matter, the density of which is unequally distributed, will not 



