From: donl@glass.esd.sgi.com (donl mathis)
Newsgroups: sci.astro
Subject: Re: Refurbishing Observatory...SURPRISE !!
Keywords: telescope
Date: 26 Jan 93 00:43:14 GMT
Reply-To: donl@glass.esd.sgi.com (donl mathis)
Organization: Silicon Graphics, Inc.


In article <1993Jan20.020718.14371@adx.adelphi.edu>,
jf4527@adx.adelphi.edu (Jamie Fitzpatrick) writes:

|> until I was ready to tackle the cleaning job on it that I realized
|> it was something special. It had all brass fittings. On the front
|> was inscribed..." Alvin Clark & Sons    1877     Cambridgeport Mass."
|> Does anyone know who this was ? I've removed all the brass an found
|> a second lens (7 inches) packed in a brass container.

I might recommend "The History of the Telescope", by Henry C. King.  A
very interesting book, if you like telescopes.  The famous names and
instruments we have heard about take on new life when you know some of
the stories behind them.  I shall bodily lift a summary of various
passages on Alvan Clark & Sons; I hope a few people find it all as
interesting as I did.

----

Alvan Clark was a portrait painter who was interested in telescope
objectives, and spent enough time grinding lenses and mirrors to
discover that it was a difficult thing.  He had heard of the quality of
the 15 inch European objective in the telescope at Harvard, and was one
day granted the opportunity to look through it.

	"I was far enough advanced in knowledge of the matter to
	perceive and locate the errors of figure in their 15-inch glass
	at first sight.  Yet these errors were very small, just enough
	to leave me in full possession of all the hope and courage
	needed to give me a start, especially when informed that this
	object-glass alone cost $12,000."

He closed his studio, started out by figuring existing lenses, and then
started grinding his own.  He made a 5 1/4 inch achromat, and then an 8
inch, and knew by his tests that they were at least as good as, if not
better than, what the Europeans were producing.  This was in about
1844, and for the next seven years he worked without getting much
business.  He started corresponding with Dawes about the double stars
he was resolving with his objectives, and Dawes became quite enthused
about them, buying several, including an 8 inch that was lated passed
to William Huggins, who used it for most of his pioneering work in
spectroscopy.  Dawes invited Clark to London to meet Lord Rosse and Sir
John Hirschel, which provided significant publicity for Clark.  The
news of the wonderful telescopes and the things being done with them
spread, so that when he got home to America, he was swamped with
orders, and his business was off and running.  The shop moved and grew,
and became "Alvan Clark & Sons".

In 1860, Dr. Barnard ordered an 18 1/2 inch achromat for the University
of Mississippi, which at the time was (I believe) the largest
refracting telescope ever made, and Clark accepted the job.  He sold
his house, bought some land, and built the first American telescope
factory.  His sons designed and built the grinding and polishing
machines.  There was a 230 foot long tunnel under the factory to be
used for testing, where vibration, dust, and humidity could be
controlled.  The bought the two pieces of glass from Europe (because
getting good glass that big was another problem in itself), and spent a
year or so grinding and polishing.  During rough testing, with the
glass mounted in a temporary tube, they pointed the glass at Sirius,
and noticed not one star, but two, the second being a faint companion.
This was a Big Deal, and quite an amazing thing.  Because of the civil
war, the glass never reached the university, and ended up at the
University of Chicago, to be used by Hough and S. W. Burnham, and then
on to the Dearborn Observatory at Northwestern University in Illinois.

In 1870, the government wanted the Clarks to build an objective for a
telescope for the U. S. Naval Observatory, the biggest telescope they
could get for $50,000 (in 1870 dollars!).  The size ended up being 26
inches, and the Europeans had real trouble producing good pieces of
glass that large.    Grinding started in 1871 and took a year and
half.  The focal length was over 32 feet, and the cost $6000.  This
lens nearly reached Dawes' limit of 0".16 on close doubles, and was
used in the discovery of Deimos and Phobos.  The lens, remounted in
another telescope, was apparently still in use in 1955.

The Clarks made many other notable refractors and/or lenses: a 15.6
inch for the University of Wisconsin, a 23 inch for Halstead
Observatory (now of Princeton University), a 16 inch for a private
party, another 26 inch for the University of Virginia, a 30 inch for
Pulkowa Observatory, the 11 inch achromat with a photographic corrector
used to take the first photograph of the Orion nebula, a 20 inch for
Wesleyan University in Connecticut, a 20 inch for Chamberlin University
in Colorado, and the 24 inch for Percival Lowell, a wealthy amateur who
studied mars.  Also, the 36 inch Lick refractor and the 40 inch Yerkes
refractor, of essentially the same design with the mounting produced by
the same person.  The glass for the 40 inch cost $20,000, and was
originally intended for the University of Southern California, which
couldn't get the money to finish the job, and the glass ended up,
through the efforts of George Ellery Hale, in Chicago, with help from
Yerkes.

And others.  Producing large pieces of raw glass was a genuine problem
in those days (and still is, but the rules and dimensions have
changed!).  Grinding and figuring *any* telescope objective was a bit
more difficult without all the technical support we now have, and
making large ones was an even more significant task.  These are special
lenses.

- donl mathis at Silicon Graphics Computer Systems, Mountain View, CA
donl@sgi.com
Newsgroups: sci.astro