Flamsteed Astronomy Society

“The Other Six” — The World’s Great Refractors

  June 9, 2005

NUMBER 9 — 28-in Great Equatorial by Grubb, Royal Observatory Greenwich 1894

The back-marker in the list of the largest refractors ever made is, of course, our very own 28-inch Great Equatorial at Greenwich.  Commissioned by William Christie  [ More], the object glass (OG) was built by Sir Howard Grubb in Dublin [ More].  It was designed to be a photo-visual refractor.  A lens element had to be reversed to convert from one to the other, but this procedure didn’t work well.  The 28-inch was left configured for visual work and photography switched to the 26-inch Thompson Refractor (gift of surgeon Sir Henry Thompson [ More]) now at Herstmonceux.  The glass blanks for the 28-inch lens came from the Chance Brothers in Birmingham.  Their business had benefited from the help of a defector from the Guinands.  In 1894 the 28-inch was mounted in the existing English Equatorial mounting made for Sir George Airy in 1859 to house the 12.75 inch Merz.  At 28-feet, the 28-inch was too long, though, to fit in the existing dome and a new dome of the present onion-shape was built from papier-mâché to house it.

On with the countdown.   The text contains links to the relevant websites for more information.

NUMBER 8 — 30-inch by Clark, Pulkovo St. Petersburg, Russia 1885

Next up (really equal 6th) and oldest in the list, comes the Clark’s 30-inch at Pulkovo Observatory near St. Petersburg Russia.   Pulkovo was founded in 1839 by Wilhelm Struve from Dorpat.  He started a dynasty of astronomers.  He was followed at Pulkovo by his son Otto who commissioned the 30-in opened in 1885.  At over 50 feet focal length, it was almost twice the length of the Greenwich refractor, and remained the world’s largest for two years.  Sadly the Pulkovo 30-inch doesn’t survive today.  It was destroyed in the fighting for Leningrad during the Second World War and although the observatory has been re-built, the telescope itself has not.   The 30-inch lens does survive in the Pulkovo Museum.

NUMBER 7  — 30-inch William Thaw Telescope by John Brashear, Allegheny Observatory, Pittsburgh PA 1914

Number 7 is the youngest in this list, the 30-inch by Brashear at the Allegheny Observatory in Pittsburgh.  Railroad tycoon William Thaw was friendly with observatory director Samuel Pierpoint Langley, and had donated generously to the observatory.  The 30-inch was the gift of his son in his memory in 1914.  It is a photo-refractor of 46-feet focal length and was used for one of the most extensive studies of stellar parallax.

NUMBER 6 — La grande Lunette Bischoffsheim 30-inch by Paul Gautier and Henry Bros., Cote d’Azur Observatory, Nice, France 1887

Number 6 is a personal favourite for architectural elegance.  The 30-inch by French team Paul Gautier and the Henry Brothers was opened at the Cote d’Azur Observatory near Nice in 1887.  In the end, the Gautier/Henry team offered the only serious competition to the Clarks.  The observatory was funded by Raphael Bischoffsheim, heir to a firm of Paris bankers (No John, the collective noun is not ‘wunch’).  At 59 feet focal length, la grande Lunette Bischoffsheim is more than twice the length of the Greenwich refractor and was equal largest in the world for a year.  The dome was engineered by the great Eiffel.  The dome sits in a hydraulic bath which supports the weight evenly.

Read On —

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