Ansbro, Eamonn, 1980

              DEPARTMENT i
Mr. Eamonn Ansbro
"Dunowen"
Clontarf, Dublin 3
Ireland
Dear Mr. Ansbro:
t£*lco R
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Brady's prediction of a 10th planet appears to be hopeless, because it was
based on a few days delay in perihelion time of Halley's comet, and a few
others. Comets are subjected to non-gravitational forces, such as jets of
gas escaping from the nucleus near perihelion, imparting thrusts like a
rocket engine, which modify the orbit.
Nevertheless, an exhaustive search was made by Dr. Henry Giclas at the
Lowell Observatory, using the 13-inch astrograph that I used 1929-1945, to
the 17£th magnitude over a large area beyond my last strip. Brady predicted
that his large planet would be several magnitudes brighter than Pluto, which
would have been relatively easy to find, but Giclas found nothing of it.
The angular momentum of such a massive planet (3 times that of Saturn) with
an inclination of 120 degrees (60 degrees retrograde) would have pulled the
orbit planes of all the other planets into its plane within a period of one
million years. Thus the evidence is overwhelmingly against the existence of
such a planet.
Enclosed are sheets indicating the large sky areas that I searched to
magnitude 17§. Note the sheet from Norton's Atlas, on which I had traced my
plate boundaries.
It appears that your Super-Schmidt 11/16 inch //0.5 is totally unsuited for a
planet search. A fast focal ratio limits the exposure time to only a few
minutes because of the rapid build up of night sky fogging. Thus, the capacity
to record faint magnitudes by long exposures is denied. In fact, the capacity
to record fainter magnitudes is proportional to the square of the focal length.
Your instrument could scarcely reach fainter than magnitude 13.
To conduct a planet search to a significantly fainter magnitude limit beyond
what I did would require an fl  Schmidt with a focal length of 90 to 100 inches.
You would encounter 7 to 10 times more stars. Since the work of blink-examination is proportional to the number of star images to inspect for planetary
shift in position, you would have to spend about 50,000 hours at the Blink-
Comparator to cover the sky area that I did in 7000 hours!
I found a 7-power magnification to be the most practical one in blink-examination. I tried 10-power, but it slowed the work of examination, because the
plate grain is over-magnified and is distracting.