IELIIOLARE 
[APRIL 22, 1897 
lens is better than is assumed by various astronomers ; I 
found it about ten times greater than it is given, for in- 
stance, by Prof. Wilsing in his recently-published paper 
in Astr. Nachr., No. 3400. 
The weak point in photographing stars and nebulz is 
not in the instrument ; it is in the plate. We know that 
the Pleiades are surrounded by wide-spread nebulosities, 
shown by Prof. Barnard and myself. Now for four years 
I have been working at a chart of this nebulous region, 
but it has been impossible to get to an end till now. In this 
case the plates did not allow it; either they were not 
sensitive enough, so that I got nothing, or if they were, 
they had streams or spots looking exactly like nebule. I 
made several dozens of exposures of the Pleiades, some 
of twelve hours’ exposure, containing beautiful nebu- 
losities, but no plate has been sufficient. All of them 
show, besides the true nebulosities, more or less artificial 
nebule, making it impossible to find out exactly the 
structure of the true nebulosities. Thus we need often 
a large number of plates to get the true nebulosities 
ready for charting. This is now the chief question for 
celestial photography. 
Photographs of small nebulee taken with portrait lenses 
often show much detail ; for instance, the nebule near 
y Cassiopeie, called by Barnard the “fan-shaped” 
nebula, These nebulae were photographed the first time 
Fic, 5.—Fan-shaped nebula in Cassiopeia, 
by myself, December 30, 1893, and described in the 
Astr. Nachr., No. 3214. Prof. Barnard obtained them 
several weeks later, and he showed that these nebule 
represent a good example for the advantages of portrait 
lenses over reflectors in discovering nebulze, because Dr. 
Roberts did not find them on his plates. Now these 
nebulze seem to me of the greatest importance for the 
comprehension of the genesis of stars ; and especially for 
the theories of Mr. Lockyer, these will be found very 
interesting objects. Several years ago I gave in Asér. 
Nachr., No. 3217, an illustration of one of those nebulz 
[o" 52™ + 60° s/ (1860)], and the sketch is reprinted here 
(Fig. 5). I have shown that the nebula looks like a 
tornado, in the concentrated part of which the stars are 
formed, and that thus the chain formed by the stars may 
be understood. 
There we have the point where our small portrait 
lenses fail, and where the reflector finds its place. The 
lens has found the nebula, and given the first idea of its 
constitution ; but the large mirror will bring out here the 
details necessary for our knowledge. It is the same as 
with the small spiral nebulz, of which Dr. Roberts’ 
plates have shown us the true form, 
To me it is quite incomprehensible how it was possible 
to begin a dispute about the use of the portrait lens in 
celestial photography. The portrait lens has given us so 
much, that it is now too late to discuss its efficiency, 
NO. 1434, VOL. 55| 
The doublet finds the nebulee—I will not speak of comets, 
planets, &c.—and throws light upon the ways in which 
the large nebulous streams spread over enormous parts of 
the sky. The charting and following of these streams forms 
now one of the most important problems of astronomy. 
Therefore this instrument is absolutely necessary for us. 
It brings us also to a certain high degree of knowledge 
of the finer detail, though not nearly so high as the mirror. 
But with portrait lenses not too large we can expose very 
long, and over several nights, so that we can get traces of 
nebulz and stars, which we can never find with the large 
reflector, because such very long exposures are not quite 
possible with a reflector, for technical reasons. 
For these points the reflector has to recede. It is true 
the portrait lens will often photograph certain objects as 
nebulous, which will be found later formed by smallest 
stars. But the pictures of the reflector show, likewise, at 
many places nebulosities which, I am sure, are composed 
of relatively bright stars. An example of this effect has 
been given by Prof. Barnard, for the case of Dr. 
Roberts’ plates (A/onthly Notices, \vii. No. 1). The 
difference between the two instruments in this direction 
is not a very great one, and because the portrait lens is 
absolutely necessary to us in so many problems shown 
here, we have to use it as often as we can for these pur- 
poses, and to leave the reflector to work out the finest 
details of special points. Max WOLF. 
Heidelberg, Astrophys. Observatory, March 1897. 
THE TWENTY-FIFTH ANNIVERSARY 
THE FOUNDATION OF THE 
ZOOLOGICAL STATION. 
ays April 14 was celebrated, with great ceremony and 
éclat, the twenty-fifth anniversary of the foundation 
of the Zoological Station at Naples by Dr. Anton Dohrn. 
To the general outside public, the eventful day itself 
was heralded by the appearance in the Bay, just opposite 
the Zoological Station, of the entire fleet of the Station, 
drawn up in line, and gaily decked with bunting. This 
consisted of the two steamers, the Johamnes Muiiller and 
the Frank Balfour, and five small fishing-boats. In 
addition, the Italian Government sent a guard of honour 
in the shape of a second-class cruiser, the /¥eramosca, 
which remained in attendance all day. 
In the Station itself all was excitement and expectancy. 
In the morning, a deputation consisting of one German 
one Italian, and one Englishman, who were supposed to 
represent the naturalists of each nationality at present 
working at the Station, waited on Dr. Dohrn, and offered 
appropriate congratulations, each speaking in the lan- 
guage of his nation. Dr. Dohrn, on replying, successfully 
evaded linguistic difficulties by beginning his speech 
in German, continuing it in Italian, and finishing it in 
English. The same deputation also waited upon and 
congratulated Dr. Hugo Eisig, Dr. Dohrn’s senior as- 
sistant, who has been associated with him since the 
foundation of the Station. ’ 
The grand ceremony itself began at two o'clock. The 
visitors, on arrival, first assembled in the library, and 
then passed on to the meeting-room, which was situated 
on the ground floor of the smaller building. This was the 
largest room available, and it held about one hundred and 
twenty people. Needless to say, every available seat 
was occupied. At one end of the room was a small 
platform and desk, from which the various speakers in 
turn delivered their discourses. Just above the desk was 
hung a specially-painted picture, representing the Bay of 
Naples, and in the foreground a symbolical figure resting 
against a block of stone, on which was inscribed, “Al 
Prof. Dohrn ed ai suoi cooperatori,” and the fact of the 
twenty-fifth anniversary. Ona shelf running round the 
end of the room were arranged the various addresses 
OF 
NAPLES 
