Tuesday, March 9, 2010

Alvan Clark & Sons--telescope makers

US Naval Observatory's 26" telescope.

Lick Observatory's 36" telescope

Yerkes Observatory's 40" telescope

Bill Ashworth [Linda Hall Library Newsletter] wrote...

Alvan Clark, an American lens maker, was born Mar. 8, 1804. With his sons, Alvan Graham and George Bassett Clark, Alvan senior founded a telescope manufacturing company, Alvan Clark & Sons, and, beginning in 1862, they turned out the best and largest refracting telescopes in the world for the next forty years. The telescope built for the U.S. Naval Observatory had a lens 26" across, and was used to discover the two moons of Mars in 1877. The telescope for the Lick Observatory, opened in 1888, was 36" across, and was the first installed on a mountain top. And the Yerkes refractor, 40" across, was inaugurated in 1897, and it is still the largest working refractor in the world.

And from Backyard Voyager...

The Clark family built their first telescope in 1844 when the eldest son George brought home a broken dinner bell from school, and melted the metal down to create a mirror for a reflecting telescope. His father, Alvan, became so interested in the project that telescope creation became a hobby that within two years evolved into a family business that endurd for nearly a hundred years.

During the second half of the nineteenth century, due in part to advances in optical glass technology, the trend toward reflecting telescopes rather than refractors was reversed. By then, astronomy had become an important part of the popular culture, and affluent industrialists were keen to finance colleges with observatories and even telescopes bearing their names. To them, of course, bigger was better, which was fortunate for the astronomers who would use the instruments. This trend coincided with the emergence of the company started by Alvan Clark and his sons, George and Alvan Graham. In those days American telescope makers were still taking a back seat to Europeans, but it wasn't long before astronomers the worlkd over took notice of the quality of the Clarks' work, particularly in their ability to create very large aperture, research grade achromatic lenses. They became the first significant American contributers to the creation of astronomical instruments. Almost every large observatory in America and many throughout Europe housed Clark telescopes.

Five times during their lives the Clarks produced the world's largest refractors. One of them, the U.S. Naval Academy's 26" refrator is still in use today as a research instrument. The second largest was the 36" refractor in the Lick Observatory in California. In 1897 the Clark's largest telescope was completed, the 40" Yerkes, which is to this day the largest refracting telescope ever produced. Its tube is 63 feet long and the tube and mount weigh over twenty tons. A hydraulic floor was built to raise or lower the observer to the eyepiece.

Much has been written about the Clarks' contributions to astronomy.Alvan Clark was said to be so sensitive to imperfections in glass that he could feel a lens with his thumb and find flaws that were invisible to the naked eye. He used his thumbs and optical rouge for the final polish. Their skill was so great that those of us in the 21st century can still have opportunities to observe the skies through their near perfect lenses, since many of these durably built instruments are still in use.

There are said to be more than 600 of their telescopes accounted for. Smaller Clark refractors still turn up from time to time, scopes that had dropped out of memory for decades. Two weeks before this writing, someone sold a 3" Clark refractor on Ebay for $3400.00. The seller found the scope in his attic, where it had been for over seventy years. Like so many other Clark scopes it is in excellent working order.

Alvan Clark & Sons [Wikipedia]

No comments: