62 



KNUT LUNDMARK, GLOBULAR CLUSTERS AND SPIRAL NEBUIJE. 



parallax. The only doubtful hypothesis to be introduced is that the mean maximum 

 absolute magnitude is the same for the novae in the Milky Way as well as for 

 those in the spiral nebuhe, and at present there is nothing to be found that speaks 

 against such a supposition. 



The last parallax-value is of interest as being of the same order of magnitude 

 as the preceeding one. Considering the somewhat uncertain suppositions on which 

 its calculation is based I have nevertheless not wanted to assign to it any great 

 importance. 



The present investigation has given as the main result that the spiral nebulce must 

 be considered as situated at considerable distances jr om the solar system. Whether they 

 are Jeans' star-producing mechanisms or remole galaxies is, on the other hand, more 

 difficult to decide. Possibly ive might in the present jaets see a suggestion that the 

 latter is the case, hut the spiral nebulce do not, however, seem to be oj such dimensions 

 as those that should be ascribed to the galactic system with regard to Shapletfs investiga- 



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Fig. 11. The relation between parallax and total magnitude for spiral nebula?. 



tions, and much also speaks against regarding the Galaxy as having a stueture, ana- 

 logous to that oj the spiral nebtdee. 



Finally I have, under the supposition that the true dimensions of spiral nebulse 

 are on an average of the same size, derived relative parallaxes for the large spirals 

 from measurements of their apparent diameters. Certainly this supposition is less 

 justified here than concerning globular elusters, as it seems to be evident, that spiral 

 nebulse may be divided up into several types, but on an average the supposition 

 will nevertheless be correct. Another mean of obtaining the relative parallax we 

 have in the estimations of the total magnitude of nebulae, performed by Holetschek, 

 Kritzinger, Stone, and the Strassburg observers. The total magnitude of a 

 nebula is a function of its surface intensity, its extension and its condensation, and the 

 smaller the nebula is, the more the total magnitude tends to approach the conception 

 of står magnitude. Therefore it is evident that the total magnitude does not vary 

 with the parallax in the same way as the apparent diameter. The relation — given 

 in the curve above — between %, calculated from the apparent diameters, and the 

 total magnitude m, is derived from the 59 nebulre in the table XIV. 



