Universitätsbibliothek Heidelberg, Heid. Hs. 3695 EC4,4 Campbell, William Wallace; Wolf, Max [Adr.]: Briefe von William Wallace Campbell an Max Wolf: Brief von William Wallace Campbell an Max Wolf (Mount Hamilton, 22.7.1903)

2. Should an instrument devoted to this line of investigation be
located, if possible, where the number of clear nights is large and the
atmospheric conditions are good, in order that a series of observations
may be continuous, or nearly so, throughout the period of a star's vari-
ation?
3. Is a very powerful telescope needed in order to follow spectra
through their minimum brightness?
4. Is it desirable that a large range of spectrum he available,—
perhaps from Ha in the red to the ultra-violet limit set by our
atmosphere?
5. Would you recommend a large reflecting telescope for this pur-
pose? If so, do you recommend that the parabolic mirror be larger than,
equal to, or smaller than four and one-half feet (1.37 meters) in dia-
meter*? Is the construction of such an instrument perfectly feasible?
6. Should spectrographs be provided such that all portions of the
spectrum could he studied under the highest dispersion practicable?
7. Should spectrographs be mounted near the lower end of the
telescope, for greater accessibility? What form of mounting for a large
reflecting telescope would you recommend?
8. Should stars under investigation be observed simultaneously
with photometers, as accurately as possible? (It would not he planned to
duplicate unnecessarily any photometry now so well done at Harvard,
Potsdam, or elsewhere).
9. Should provision be made for the prompt publication of results?
10, Would a force of one Astronomer and three Assistants he larger
tuan necessary for the efficient use of such an equipment?

Thanking you for such answers and comments as you may supply, I am
Yours very respectfully,