Universitätsbibliothek Heidelberg, Heid. Hs. 3695 EL 90,6 Lowell, Percival; Lowell Observatory (Flagstaff, Ariz.); Wolf, Max [Adr.]: Briefe von Percival Lowell an Max Wolf: Brief von Percival Lowell von Lowell Observatory (Flagstaff, Ariz.) an Max Wolf (Flagstaff, Arizona, 22.4.1916)

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April 32,).916.

Professor Max Wolf, Director,
Astropbysikalisches Institut,
Heidelberg, Germany.

Dear Professor Wolf:

Your charts of photographs of the sky with the

16-inch Bruce doublets are frequently used and we have been

impressed with

their excellence and great value.

It has

occurred to me

that since you have two of these objectives

it may be that you are not using both of them, now that photo-

graphic =_
E "
the fi 1!'
making :Z
same sc^E-
E-
— o
lies in J=_r
photogr
u u d a r t a I'E
zz co
bopelesi!=
For som<]E
survey. E-
= (0
of five E
scale i
t r. e 40- E
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w 1.th th. =
and lab E-?
doublet ="


ived quality and defects of
blesome as formerly thereby
graph fields in duplicate on


[ot using both of the doublets
jow much in need of a first-class
Mis size, but the matter of
] at the present time seems
fulty of obtaining optical glass
!d in an extensive photographic
Made with a Brashear doublet
is instrument, however,the
has also been covered with
ited field of good definition
ts any extensive survey slow
tad the use of the 9-inch
Observatory. During the