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

Dr. Llax Wolf, 2.
of the wave-lengths will come very nearly to the same focus. Your ex-
periments on the effect of interposing screens of various kinds so as X
to cut off a portion of the star imago are extremely interesting, as
showing that the spreading of the star image is not due to any import-
ant effect in the photographic film itself. It seems to me, however,
that this effect can be perfectly explained without supposing that the
lenses themselves have any defect; indeed it would naturally follow
from the fact that the diffraction pattern from a point of light is in
reality an Infinite area; and more and more of this will be impressed
on the plate as the tune of exposure is lengthened. I have not investi-
gated the effect as yet quantitatively to see whether it is sufficient
to completely explain the phenomena of the enlargement of star images,
but expect to take it up very soon. Some preliminary results which I
have obtained are referred to in a paper which appears in the present
(August) number of the Astrophysical Journal.
I am very much interested in the problem of meteor photography,
and am collectng all the references that I can find to experiments that
have been made in this direction. Would you kindly tell me whether you
have ever made any experiments yourself, and if so, where they have
boon published if they have been published at all? Or whether you have
ever accidentally obtained any meteor trails on plates that you have
exposed for other purposes. In the latter case I should be very much
interested in knowing the aperture and focal length of the lens with
which the results were obtained.
Very truly yours,