142 TEN-INCH DIFFRACTION GRATING. 



a million waves, such as grating would have a resolving power 

 exceeding a million. 



This investigation has had assistance from the Bache Fund of 

 the National Academy of Science, from the Carnegie Institution, 

 and from the University of Chicago. 



In addition to the grateful acknowledgment to these institutions 

 I would add my high appreciation of the faithful services rendered 

 by Messrs. Julius Pearson and Fred Pearson. 



