( 698 ) 



1^' . Because, since the publication of tlie paper mentioned, our 

 lyiowledge about the sun's velocity has made considerable progress; 



2"<^. Because in its derivation a slight mistake was discovered. 



I shall not apply any correction, however, because the two cor- 

 rections nearly compensate each other for the magnitude 8.75. There 

 is a fair prospect of the possibility of materially improving the values 

 given in Publication 8 before long. It seems advisable to wait for 

 such improvements before we alter these determinations. 



If for this reason we provisionally adopt the value (5) we get : 



Mean absolute parallax of the 168 nebulae 



0"0046 ± '0012 (p. e.) (6) 



This result is somewhat less reliable, however, than (5) because 

 of the additional uncertainty in the absolute parallax of the stars of 

 comparison. 



The value (6) agrees nearly with the mean parallax of the stars 

 of the tenth magnitude. 



I shall not insist on the exact amount brought out for the parallax. 

 I shall only direct the attention to the fact that from observations 

 covering only a period of somewhat over thirty years, we get a 

 probable error of hardly over 0".001. If this is the case with visual 

 observations we may look for really excellent results by photography. 



The best measurable nebulae must be generally the smaller ones. 

 The number of these which can be photographed is enormous. 



With his Bruce-telescope (opening 40 centim., foe. di.st. 202 centim.) 

 Max Wolff obtained in 150 minutes a single photograph of the 

 region near 31 Comae, containing 1528 measurable nebulae (Publ. 

 Königstuhl I p. 127). 



This richness of matei-ial will enable us to confine ourselves provi- 

 sionally to those nebulae which allow of a very accurate measurement. 



Personal errors must disappear because we shall certainly succeed 

 in nearly every case in making our pointings on the same point for 

 the several epochs. The peculiar p. m. will be the more thoroughly 

 eliminated the more extensive our material; especially if this material 

 is distributed over the whole of the sky. Errors in the precession 

 have no influence at least on the value of the relative parallax. 



I am convinced that by photography we may obtain, even within 

 ten years, results which will far surpass in accuracy those of the 

 present paper. Thus we may hope, in the near future, to reach 

 a fairly satisfactory solution of the vexed question respecting the 

 position of the nebulae in space. 



The same treatment to which we have" here subjected the nebulae 

 may of course also be applied to other objects. We have already 



