6. _Wave Lengths_.--The determination of the wave lengths of the lines
in the stellar spectra will form an important part of the work which has
not yet been begun. The approximate wave lengths can readily be found
from a comparison with the solar spectrum, a sufficient number of solar
lines being present in most stellar spectra. If, then, satisfactory
results are obtained in the preceding investigation, the motion of the
stars can probably be determined with a high degree of precision. The
identification of the lines with those of terrestrial substances will of
course form a part of the work, but the details will be considered
subsequently.

From the above statement it will be seen that photographic apparatus has
been furnished on a scale unequaled elsewhere. But what is more
important, Mrs. Draper has not only provided the means for keeping these
instruments actively employed, several of them during the whole of every
clear night, but also of reducing the results by a considerable force of
computers, and of publishing them in a suitable form. A field of work of
great extent and promise is open, and there seems to be an opportunity
to erect to the name of Dr. Henry Draper a memorial such as heretofore
no astronomer has received. One cannot but hope that such an example may
be imitated in other departments of astronomy, and that hereafter other
names may be commemorated, not by a needless duplication of unsupported
observatories, but by the more lasting monuments of useful work
accomplished.

EDWARD C. PICKERING,

_Director of Harvard College Observatory_.