Universitätsbibliothek Heidelberg, Heid. Hs. 3695 EW 5,1 Wadsworth, Frank Lawton; Wolf, Max [Adr.]: Briefe von Frank Lawton Wadsworth an Max Wolf: Brief von Frank Lawton Wadsworth an Max Wolf (Williams Bay, Wisconsin, 2.8.1897)

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ARCTURUS CHiCAGO
CUBH)
Herrn Professor Dr. Max Wolf,
Observatorium, Heidelburg,
Germany.
Dear Sir,-
In a paper of yours which was published in Nature of April
22, 1307, you have discussed the relative advantages of portrait lenses
and reflectors in celestial photography. I have recently been very
much interested in tit is subject myself, and have published a paper
which appears in the August number of Knowledge, and also in the Astron-
omische Nachrichten, bearing on this same question. At the time this
paper was written I had not had an opportunity of reading yours, (as
our numbers of Nature frequently do not reach us for several weoKs after
they have been published), You will see in the paper in Knowledge that
I differ from you as to some points in regard to stellar photography,
particularly as to the cause of difference between stellar images given
by the reflecting and portrait lens. If the portrait lens is properly
corroctdd for spherical aberration, I cannot believe that there can be
any essential difference between the star image formed by it and the
star image formed by a reflector, so far as its effect on the photo-
graphic plate is concerned. Of course there will be a very decided dif
ference in the two images if we consider the effect of light of all
wave-lengths, because of the chromatic aberration of the lenses. Put
over the small range to which the photographic plate is sensitive all