86 NATIONAL ACADEMY OF SCIENCES 
of a protuberance fell upon the slit, so large a portion of its light was monochro- 
matic that the hydrogen line C appeared as a bright line in the corresponding 
portion of the spectrum. If now the slit was widened, the form of the protuber- 
ance became visible. By placing a second slit so as to cut off all portions of the 
spectrum except that of the line to be studied, replacing the eyepiece by a photo- 
graphic plate, and giving similar motions to the latter and to the image of the sun 
on the slit we have the spectroheliograph. The principal credit must be given 
to Professor Hale for the independent invention of this instrument, for excellence 
in the plans of its mechanical construction, for skill in its use, and for the final 
results obtained with it, although as almost always happens, a portion of the 
credit must be given to other astronomers who were pursuing the same line 
of work... a). 
“Professor Hale has shown the same skill in invention, construction, and 
application in the other portions of his work. The problem of photographing the 
spectra of the stars of the third and fourth types is one of unusual difficulty. 
D 4b ~ wenne Uinhe anllantine nawer of the sn-inch refractor. and the use 
National COUNCIL OT TNE AssOcialiol UL MLauUCIIIes anu as bepie 
For the full report, see Rep. Nat. Acad. Sci. for 1904, pp. 14-15. 
