The San Francisco call., 1909-12-02
Complex Instrument for Taking Pictures Of the Sun
Added to the Astronomical Modern Equipment
By REV. IERuME RIcARD. S. ].

surfaces This unpleasantness is now
avoided by using a biplanar lens. with
possibly an infinitesimal amount OF sill
yer in it's composition. one surface be-
ing given an extremely high. polish.
such lens will. Of course give two
reflections, one from the highly pol
ished side. another from the dun side
If these two reflections proceeded in
the same direction. as would happen if
the sides We're parallel, they would
certainly spoil the image on the ground
glass To escape this Inconvenience
the biplanar is cut thicker on one side
than on the other. which turns the
whole thing into sort Of prism and by
which the reflections are made TO fol-
low out different directions. Both these
reflections can equally well be made to
strike the ground glass. The effect.
however. is different; one is spectral
and ghastIy, with the eolors OF the
rainbow about it; the other is pure,
sharp, beautiful even as the original.
with its violet patches and famboyant
Iuminosities-vulg called spots and
faculae.--
But the thing which most arrests the
attention in a solar photographic tele-
scope is the camera end. The violence
exerted by the spring or by hand or
by gravity in making the inhnitesimai
exposure is sure TO make the camera
tremble at the very moment when the
most absolute stiffness is Imperative.
The only remedy is complete separa-
ton between the exposing slide and
the plate carrier. and separation not
simply where the act is performed. but
from very bottom to very top Of the
observing room, for those vibrations
are so insfdious that they penetrate
everywhere.
Hence a well insulated column OF
solid material is to rise from way down
in the ground to-a suitable height to
receive the plate holder. so that its axis
will coincide with the optical axis OF
the photo lens and that of the tube.
while the shutter frame is firmly pin
ioned to the wall where the tube abuts-f
This done there is no other way of pos
sible ntercOmmunication save through
the camera bellows. But the latter is
the very contrivance which is best cal
culated to keep good guard and ward
of the unwelcome visitors.
We were Just forgetting another
thing which has been found bother
some. A pencil of light crossing
dark medium walled all around loses
some of it's Photographic efficiency BY
reflections of .diffused light from the
very walls that had been doctored up
to the finest point to increase their abb
sorptive power. Hence certain OBJ
structions called diaphragns must be
judiciousIy distributed throughout the
whole length OF the tube. Our own
has five such wall reflections inter-
ceptors with apertures 10. Il. IA. 1s
and IS inches. respectively, going from
north to south.
Another thing of which one would
never think at first, but which in the
end proves matter OF absolute neces-
sity. is little window at the north end
of the tube just a short distance above
the photo lens. through which the oper-
ator can see whether the objects
image falls at all on the ground glass
and whether it is properly eentered
This corresponds TO the ability 70 point
properly from the eye end in a visual
telescope AS that window must be
light tight and be closed immediately
after eentering the image the best kind
of a thing to have is a very small
plate holder, the slide of which can be
utilized for opening or shutting We
will conclude this little sketch of the
photoheliograph by stating that we are
thoroughly pleased with the excellent
performance of the one which has
been lately erected at the college OBJ
servatory TO be fitting companion 10
the four inch comet searcher and the
eight inch equatorial for general pur-
poses. The reflector and eight inch
fat surface is most powerful and as
good as we could wish; the photo lens.
six inch objective. is equally good. The
siderostat, Cooke style, is very com
pact, solid and weatherproOf and per-
mits an operation almost from horizon
east to horizon west. besides command
ing a large amplitude in declination.
The plate carrier IS a solid plane of
massive iron that nothing can shake
The bellows is vibration proof and the
exposing slide or shutter, now changed
from push to a pull. travels with
almost lightning speed making an ex-
posure easily from 1900 to 1-1000 OF
a second.
In order to make perfectly sure OF
this exposure time we have managed
two electrical contacts one for the
start. another for the arrival OF the
shutter. both of them in touch with the
astronomical chronOgraph on which.
by means of a vernier scale very small
fractions of a second can be counted.
Thus. If the time of flight of the slide
across the whole width Of the ground
glass Is, say. one-fftieth of a second.
and the width OF the side split is.
say. lilo of that of the ground glass.
we have lie of 1-50. which is 1-500.
If, moreover. the diameter of the solar
is, say. One-half OF the ground glass
width. we have to take one-half OF the
1880. which is $1,000 of a second The
optical and mechanical parts of the.in-
strument came from the shops OF W. &
ID. Mogey OF Bayonne. " j.. who.
were about three years making II and
testing its capacity. The tube IL an
excellent piece of work by Mcneil &