Refractors With the renewed interest in small refractors and more affordable instruments coming on the market every year, I thought a brief history of the refractor might be of interest. Sometimes history can provide a perspective which will allow us to better appreciate what we have rather than simply take it all for granted. One of the earliest known studies of the properties of lenses and mirrors was by an Arab mathematician known as Alhazan. He was born in Barsa around 965AD and died in Cairo in 1038AD. In 1030AD he described the results of his experiments with spherical and parabolic mirrors, lenses and other optical phenomena in his treatise Kitab al-Manazir. This work was translated into Latin by Witelo in 1270AD and was later published by F. Risner. The Latin translation of Alhazan's treatise was later used extensively by Johannes Kepler in his own optical studies. The introduction of spectacles (eyeglasses) took place in Italy around 1300AD and by the early 16th century there were optical centers in Germany and Holland. In one such shop in Middleburg, Holland, there was a spectacle maker named Hans Lippershey (c. 1570-c. 1619). Legend has it that one day Lippershey's children were playing with some of his discarded lenses and suddenly came running into his shop to tell him that they found a way to make a distant church steeple appear very close. At first doubtful, he decided to investigate and found that the children had playfully lined up two of his lenses a few feet apart while training them on a remote church steeple. No, one knows if this story is true or not but it makes a nice story nonetheless. In 1729, Chester Moore Hall devised a lens design which used crown and flint glasses which gave a relatively achromatic (color free) image. Hall's achromatic was 2.5" in diameter and had a 20-inch focal length. Hall, went against the current thinking which sided with the great Isaac Newton who stated, some 60 years earlier, that the construction of an achromatic lens was impossible. So immense was Newton's scientific reputation that no one even thought of contradicting his opinion. It wasn't until the early 1800's that Guinnand, in Germany, discovered the secret of casting consistently good quality glass blanks. His contemporary Joseph von Fraunhoefer developed the mathematical techniques of optical design. Thus, started the long and distinguished history of German optical design. Fraunhoefer went on to invent what is now known as the German Equatorial Mount and produced objective lenses of a quality almost equal to today's best achromats. His first large lens was 9.6 inches in diameter with a focal length of 170 inches and a focal ratio of f17.7. In a previous version of this paper I had written that "The telescope in which this lens was mounted was installed in the Pulkovo Observatory in Estonia in 1825 and became known as the Great Dorpat Refractor." However, a recent January, 2004, email from Jüri Ivask (Jyri.Ivask@gi.ee) pointed out that 'Fraunhofer's 9" Dorpat refractor was one of the largest in the world for some time. But it was not installed at the Pulkovo Observatory near St. Petersburg, but in Tartu (old name Dorpat) and is still located there in the museum.' See the museum page. We are grateful for the correction. This is the instrument used by F.G.W. Struve in his discovery and measurement of double stars. From these beginnings came the rush toward ever larger objective lenses and more precise measurements of great scientific importance. The next installment "I outline the refractor in America, starting with Henry Fitz and Alvin Clark. Excerpts from: 'The Double Star Observers Handbook" R.C.Tangtiay May 1998 Bill Geertsen izar@juno.com