348 E. S. Holden — Chi supposed changes in Nebula M. 17. 



vided into small squar( 



After making all the use possible of the iirst reticle, the second 

 ' 'n, and an entin ' 



diagonals. 

 " 3 second 

 btained, 



tirely new set of reference-line 

 iaking*an angle of 45° with the old set This, of course, co 

 be equally obtained by revolving the first reticle through 

 angle of 45°, but it is not quite so convenient. 



After the stars and tlie principal lines of the nebula are 

 inserted a new and higher power eye-piece is used, and the 

 ans of this. Fig. 6 is an example 



drawing is concluded by mean 



