SPECTRUM OF THE GREAT NEBULA IN ORION. 89 
and III. are omitted, for the reason that their spectra beyond K are only photo- 
graphed with great difficulty.* 
The wave-lengths of the lines of the nebula are copied from Table I., and are 
expressed on CorNv’s scale ; those of the lines in the ultra-violet spectra of stars of 
Group III. are based on wave-lengths of the ultra-violet lines of hydrogen on 
RoWLAND’s scale, according to Professor HALE.t 
The wave-lengths have been left in these different scales, because the differences 
are only minute, and, in general, in the ultra-violet region, less than the assumed 
accuracy of the wave-lengths as determined by the instruments at our disposal. 
* Phil. Trans.,’ A, vol. 184, 1893, p. 701. 
+ ‘ Astr, and Ast.-Phys.,’ vol. 11, 1892, p. 618. 
MDCCCXCY.—A 
