Sky and Telescope - October 2016 - 67

chaotic, organic and evolutionary - full of dead ends
long forgotten (until, perhaps, they revive) and instances
of three steps forward, two steps back. So here is the tale
of George Ritchey's ﬁve telescopes.

UNIVERSITY OF CHICAGO PHOTOGRAPHIC ARCHIVE (2)

1. T
The Yerkes 24-inch Reﬂector

Between 1896 and 1935, Ritchey built only ﬁve
telescopes (not including a number of specialized solar
telescopes he made for Hale, who began as a solar
astronomer). All ﬁve were very large. The ﬁrst three -
24, 60, and 100 inches in aperture - were quickly hailed
as milestones in the development of astronomy. The 100inch in particular opened new vistas for cosmic research
that left the refractor forever behind. But Ritchey's last
two reﬂectors were considered failures, and the value of
their novel design, used nearly universally today, went
unrecognized until a decade after Ritchey's death.
Viewed from a distance, the history of astronomy, and
of science in general, can look like one long, steady construction of a great ediﬁce, with each new brick being
laid naturally and logically on top of the ones before.
Look closer and the construction process is messy and

Geo
George
Ellery Hale, Ritchey's junior by four years,
was already a highly accomplished astronomer by his
mid-twenties - single-minded, ceaselessly energetic,
even frenetic, though prone to spells of depression. His
passion to build a really large reﬂector was such that in
1896, he talked his father into ordering a 60-inch diameter mirror blank from the Saint Gobain glassworks in
France, as well as several smaller blanks. One of the
latter was 23.5 inches in diameter and 2.6 inches thick.
Saint Gobain's main product was wine bottles; all the
disks were made from "wine bottle" glass.
Hale asked Ritchey to grind and ﬁgure the 24-inch.
To do so Ritchey used a grinding machine that he built
himself and operated at his Chicago home. He gave the
mirror a paraboloid ﬁgure (required for a Newtonian
reﬂector) with a focal length of 93 inches, making it an
f/4.0. He didn't have the funds to build the rest of a telescope around it, so he sold it to the new Yerkes Observatory for $200. At the time Hale was working for Yerkes's
parent institution, the University of Chicago, and he had
talked his father into paying Ritchey a salary. Soon after
Yerkes bought the mirror, it hired Ritchey onto its staﬀ,
and there he ﬁnished the rest of the telescope.
Ritchey designed an innovative arrangement for the
24-inch scope (pictured below). It could be used in two
conﬁgurations: as a standard short-focus Newtonian and
as a long-focus Cassegrain. For the latter, the ﬂat Newtonian secondary mirror could be replaced with a ﬁve-inch
hyperboloid convex mirror that reﬂected starlight back
down the tube to a ﬂat diagonal, which sent it to a focus
on the side of the tube's back end. (The primary mirror
BOUND FOR GLORY In an
1898 photo of Yerkes Observatory staﬀ, George Ritchey is
enlarged at right. George Ellery
Hale is indicated to the left. The
two men - intense, tenacious,
and eventually bitter enemies -
together built the instruments
that opened modern research
astronomy. At left: Ritchey's
ﬁrst large telescope was this
24-inch reﬂector. The Newtonian diagonal mirror in the top
of the tube could be swapped
out for the convex, hyperboloid
secondary mirror mounted in
the ring displayed on the ﬂoor.

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Sky and Telescope - October 2016

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