504 HE^RY A. EOWLAND 



lines yet appear as fine and sharp as with a lower power. If my grat- 

 ing is assumed to be perfect, in the third spectrum I should be able to 

 divide lines whose wave-lengths differed, in about 150,000, though not 

 to photograph them. 



The E line has components, about ^uwfrth of the wave-length apart. 

 I believe I can resolve lines much closer than this, say 1 in 100,000 at 

 least. Hence the idea of a limit has not yet been proved. 



However, as some of the lines of the spectrum are much wider than 

 others we should not expect any definite limit, but a gradual falling off 

 as we increase our power. At first, in the short wave-lengths at least, 

 the number of lines is nearly proportional to the resolving power, but 

 this law should fail as we approach the limit. 



