The Morse Equatorial to Altazimuth Transformer Telescope Mount
Mel Bartels, February 2013Morse's mount deserves wider attention. Here is a
representation of his design as described in Scientific American, June,
1942, Ingalls and pictured in Henry Paul's, "Telescopes for
A curved arc in the shape of a sickle attached to a tracking
tracks the telescope's tube across the sky in an equatorial arc. The
the telescope's tube is clamped to the sickle by a trolley at the
Declination. The telescope's tube pulls the altazimuth frame along with
itself. The tracking cylinder is polar aligned with the polar axis
cutting through the telescope tube's center of gravity. The tracking
cyclinder only spins: since it is attached to the ground board it
stays motionless while the rocker box rotates around it.A
curved blade representing the Declination angle is attached to the
polar axis drive which represents the hour angle. The telescope's axis
below the tube is tied to the curved blade. The altazimuth axes
intersect the polar axis. An equatorial tracking movement translates
into altazimuth motions.
Long before there were computerized altazimuth drive systems for telescope
mounts, the Morse mount mechanically translated equatorial motion to altazimuth
As explained in the Scientific American article, the idea originated with A.B.
Hendricks Jr of Pittsfield, Mass in 1936. Hendricks' idea was to link
equatorial motion to an altazimuth mount. Upon seeing this in 1936, H.F. Morse
of Southport, Connecticut devised an entirely different approach to the
He wrote that, "The object was to avoid certain inherent shortcoming in
large equatorial mountings. Estimates indicate a much lower cost. Materials
could be better used-with lessened total weight. Because there would be no
transfer of weight from one bearing to another, there would be no distortion of
parts. Because of ease and flexibility of the adjustments, less precision work
would be required on various details. Astronomers would work in an always level
position and in a constant temperature room at either end of the horizontal
axis, where light could be directed with three reflections. Because the tube
moves about the horizontal axis in one plane alone, the tube could be made very
rigid and at the same time relatively light. The whole instrument could be
floated in an annular tank of mercury, thus leaving only enough weight on the
annular track (precision ground) to insure accurate rotation around the vertical
The Sketchup model can be found at http://sketchup.google.com/3dwarehouse/details?mid=53af76a186e18e456ed97933d0fe8bb5&ct=mdsa
And we can extend the Morse transformer to eliminate field rotation
using a three axis mount like this, showing one hour tracking. Note how
the eyepiece angle is lifted up to follow the equatorial tracking arc
as opposed to above where the eyepiece angle stays horizontal.
The Great Paris Exhibition Telescope of 1900 also used an
equatorial to altazimuth transformer called a Foucault Siderostat. See
Wikipedia's https://en.wikipedia.org/wiki/Great_Paris_Exhibition_Telescope_of_1900#/media/File:Great_Ex_Telescope_Design.jpg, and Journal of the British Astronomical Association, Vol. 95, NO.3/APR, P. 89, 1985 http://adsabs.harvard.edu/full/1985JBAA...95...89M.
Conceptually linked is the Earl of Crawford's tracking arm. The length
of arm represents the Declination with the arm tying the polar axis to
the tube's axis, resulting in an identical equatorial to altaziuth
Both equatorial axes and both altazimuth axes intersecting is an
optimized design. I strongly suspect that the designers started with
less optimal designs where the equatorial portion of the transformer
was below or at the side of the altazimuth portion. This takes us back
into the rich sophisticated world of analog devices and mechanical
linkages. It also gives the modern day amateur new design possibilities.
After some thought, mental gymnastics and immersing myself in the
mechanical analog world of linkages I devised an equatorial to
altazimuth transformer where the equatorial portion is placed at the
side of the altazimuth mount. Two disks, one under the altazimuth mount
and the other at the bottom of the equatorial section, rotate against
each other such that the equatorial portion maintains its polar
alignment. The altitude arm is coupled to the curved Declination arm.
Just as in the Morse transformer proper, all four axes intersect at one
point to the side of the rocker: altitude, azimuth, polar equatorial
and Declination. Here I've scaled the polar portion smaller, albeit
As the equatorial portion tracks, it forces the altazimuth portion to
track also. Interestingly, the equatorial portion could be set free to
move as needed as the scope is aimed about the sky. This causes the
equatorial portion to act as setting circles. In fact, the field rotation angle can be read too.
Here is the change in position after one hour of equatorial tracking.
The equatorial portion maintains its polar alignment while the
altazimuth portion is forced into tracking an equatorial tracking arc
across the sky. This could be extended to a three axis mount if the
Declination car is coupled tightly to the altitude extension.
Here's the arc extended into an armillary sphere. Note that the
telescope's pointing position has changed: the hour angle is increased,
the Declination lowered, the altitude lowered and the azimuth increased.