486 

while Prof. Barnard states that “the very great 
delay in the appearance of this volume of photo- 
graphs can only be attributed to the writer’s 
anxiety to secure the best possible reproductions 
of the original pictures,” the excellence of the 
reproductions is the reward due to the delay in 
question. 
In the introduction to the volume the author 
brings together some very interesting informa- 
tion, both instrumental and photographic, with 
regard to these pioneer days. Possibly for 
the first time a statement is made regarding 
the origin of the now famous 6-in. “ Willard” 
lens, the lens so often coupled with Barnard’s 
name in celestial photography. Willard, so far 
as the author could gather, was not a maker of 
lenses, but simply a photographic stock-dealer, 
whose name was stamped on lenses made by 
C. F. Usner in New York City. These large 
lenses were used for making portraits during the 
wet-plate period of photography, their large aper- 
tures being necessary to shorten the exposure 
during portrait sittings. Their application to 
astronomical work was first made by an amateur 
who used the above mentioned 6-in. “ Willard” 
lens for photographing the solar corona during 
the eclipse in January 1, 1889, visible in Northern 
California. Some of the photographs taken were 
so excellent, and showed so well the great extent 
of the coronal streamers, that Prof. Holden, 
then director of the Lick Observatory, who was 
impressed with the excellent results obtained with 
it, purchased this lens for the observatory with 
funds provided by the Hon. C. F. Crocker. 
Prof. Barnard came to use it in the following 
manner :-— 
I had been endeavouring to photograph the star 
clouds of the Milky Way with a small Voigtlander 
rectilinear lens attached to the 6-in. equatorial, but 
because of the slowness of the lens, had secured but 
feeble impressions of these clouds. The great light 
ratio of the old 6-in. lens suggested that it would 
perhaps serve my purpose. The results of some ex- 
periments which I made with it in photographing the 
Milky Way were very beautiful and intensely interest- 
ing. When the importance of the lens for such astro- 
nomical work became apparent, Prof. Holden placed 
it in the hands of Brashear, who refigured it and 
greatly improved the definition of the star images. 
Prof. Barnard gives the dimensions of the lens, 
and as these are of interest they may be men- 
tioned here :— 
Diam. of front lens 5°85 in.=148°6-mm. 
as bach Ov Seem 7sOmm, 
Solar focus 42°59 in.=108"2 cm. 
” ” 702 ” 178°3 ” 
The distance from the rear surface of the front 
lens to the surface of the back lens was 12°8 in. 
A diaphragm of 3°83 in. aperture was placed 
between the two sets of lenses at a distance of 
5°54 in. from the front lens. 
‘The early photographs of the Miiky Way and 
comets were first made with the “Willard” lens 
in a wooden box camera strapped on to the 63-in. 
NO. 2383, VOL. 95| 
NATURE 


[JuLY .1,- 1905 

equatorial, the last-mentioned being used as a 
guiding telescope. Afterwards the lens, in its 
wooden box, was fixed on an equatorial mounting 
made by Brashear, the gift of the Hon. C. F. 
Crocker, and the telescope named after this donor. 
The frontispiece shows the instrument with the 
6-in. lens mounted, and also the Crocker dome 
which contains it. 
It should be mentioned here that the new 
mounting was not equipped with a finder, so Prof. 
Barnard had to make use of the only telescope 
which was available for the purpose. This con- 
sisted of a small telescope, having only an aper- 
ture of 2°4 in., and there was no arrangement for 
the illumination of the cross threads, so desirable 
for very dark nights. Prof. Barnard had therefore 
to employ iron wires sufficiently coarse to be just 
visible in black relief on the dark sky. By rack- 
ing out the eyepiece until the star was a little out 
of focus, he thus formed a disc, which he adjusted 
not only to be exactly behind the point of inter- 
section of the wires, but of such a diameter that 
it was eclipsed by the wires with the exception of 
four small portions which peeped out of the four 
quadrants; for “following” purposes, these four 
positions were kept perfectly equal, the slightest 
inequality being detected and corrected at once. 
Anyone who has used this method knows how 
efficient it is, provided the star used for following 
is sufficiently bright; but, as Prof. Barnard points 
out, for “following”? on a comet which has not 
a bright nucleus, ‘the following becomes a serious 
question, subject to considerable uncertainty, 
especially if the comet is faint.” This drawback 
accounts, as he remarks, for the ragged condition 
of the trails of Brook’s comet in his photographs. 
In spite, however, of the inefficiency of the follow- 
ing telescope, Prof. Barnard by his skill achieved 
wonderful results. 
Turning now to the photographs, the page 
facing each plate is devoted to details of the photo- 
graph, such as date, exposure, scale, identifica- 
tion of stars, &c., and a brief description of the 
principal features. In cases where certain plates 
call for a more detailed description, further in- 
formation is placed in the main text. 
Thus, for instance, the region of the great 
nebula of p Ophiuchi is so treated. In the de- 
scription of this plate Prof. Barnard says: “I 
do not think there is any other region of the 
heavens so extraordinary as this. . One 
hesitates at any attempt to describe it. Perhaps 
even more remarkable than the nebulosities are 
the vacant lanes that run eastward from the great 
nebula and those in the upper part of the plate.” 
These lanes, as Prof. Barnard has previously pub- 
lished, suggest strong indications of light obscura- 
tion by interposing nebulous or other matter in 
space. This remarkable region is one of many 
which were discovered by him with the Willard 
lens. The nebula of v Scorpii is pointed out as 
being of far greater interest in the direct evidence 
it gives of the obscuration of light in space. I 
Plate 3, showing the region of the great nebula 
of Andromeda, gives an example of the difficulty 
