For many years the Dearborn Telescope, the largest telescope in the world in its time, has been one of the most popular exhibits at the Adler Planetarium. The telescope has had an unusually varied career, and was recently sent out for a careful, professional facelift before resuming its place in the New Adler.

The story begins with the Civil War. In 1860 the firm of Alvan Clark and Sons in Cambridgeport, Massachusetts, received an order from the University of Mississippi for a lens 18 1/2 inches in diameter, larger than any lens in the world at that time. The objective was cast, ground, and polished, and proved of excellent quality. The timing of the order was remarkably poor for commerce between Massachusetts and Mississippi, however, and the Clark workshop found itself with a large, expensive lens and no customer.

Word of the lens reached westward to the impudent young commercial center on the prairie, Chicago. The recently formed Chicago Astronomical Society sent a representative to negotiate its purchase, supplied with a purse of ready cash. Soon the lens, properly installed in a walnut-veneered tube and poised on an equatorial mount (both by Alvan Graham Clark), adorned the Dearborn Observatory of an institution known as the University of Chicago.

The University of Chicago - not to be confused with the present one, which was established only in 1892 - foundered under financial pressures, and once again the Chicago Astronomical Society took possession of the hapless telescope. A home was created for it at Northwestern University, which in 1888 installed the telescope in to a new Dearborn Observatory near the shores of Lake Michigan.

In 1911 Northwestern decided that the lens needed a more modern mounting, and the original tube and mount were removed. In 1929 they were donated to the newly forming Adler Planetarium and Astronomical Museum, and installed on the exhibit floor. (The 18 1/2 inch lens has remained at Northwestern.)

The original tube has remained on exhibit at the Adler for decades, and was exposed to public handling for much of that time.

Attempts to protect it resulted in the addition of many layers of varnish, which eventually blackened so that the original walnut burl veneer, applied at the Alvan Clark workshop in the 1860s, was completely obscured.

In September, 1997, the Dearborn Telescope was de-installed, placed in a 270-inch crate, and carried off to Geneva, Illinois.

There the Deller Conservation Group, Ltd. stabilized the wooden coopered tube, carefully removed the layers of more recent varnish to expose the original finish, and applied a protective coating. The beautiful telescope that emerged is now back on display at the Adler, as part of an exhibition From the Night Sky to the Big Bang, celebrating human knowledge of the universe over the last millennium.