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Utzschneider and Fraunhofer Astronomical Telescope

The first achromatic lens made with two lenses of crown and flint glass was patented by John Dolland the London instrument maker, in 1757. He also eliminated spherical aberration after much experiment with the curvatures of the two lenses so achieving refraction without dispersion. The new doublet refracting telescopes were very successful and John Dolland’s paper on the subject was included by the Royal Society in the Philosophical Transactions of the Society in 1758. As a direct consequence he was awarded the Copley Medal in 1761 and elected a Fellow. However for the next five decades refracting telescopes were restricted in size by an inability to manufacture glass of perfect optical quality with a diameter of much over a couple of inches. Fine naval telescopes were made but large refracting astronomical telescopes with big diameter optically perfect objectives were not possible. The first person to successfully develop a process for making larger sizes of optical glass virtually free from blemishes was Guinand in Switzerland. Around 1805 he began using fireclay stirrers to mix the molten glass for the first time. The fireclay being porous removed the bubbles in the glass and through the stirring action kept the molten glass mass thoroughly mixed. (The fireclay stirrer continues to be important in the modern process of stirring optical glass). Enter Utzschneider who was at this time financing a business in Munich started in 1802 to manufacture high quality surveying instruments for which a supply of high quality optical glass was essential. Utzschneider was so impressed with the quality of the glass samples produced by Guinand that he persuaded him to move from Switzerland to an old Benedictine monastery at Benediktbeuern near Munich surrounded by woods for the glass furnaces with a mill-stream to supply water and there set up a glass factory with Guinand in charge. After some disagreement over the first arrangements a second agreement was drawn up in 1807, which amongst other conditions required Guinand to instruct a person nominated by Utzschneider on his secret processes. The man chosen was a young German from Bavaria named Joseph Fraunhofer (1787–1826). He was taken on as an understudy to Guinand in the making optical glass at the factory at the age of twenty in 1807. Here his enthusiasm and ability flourished. Within a year he was grinding lenses himself and soon he was given sole charge of the workshop and apprentices. Friction developed between Guinand and Fraunhofer so Utzschneider had to intervene. In 1809 Fraunhofer was put in sole charge of Benediktbeuern and made a junior partner in the firm – Utzschneider und Fraunhofer. Guinand left in 1814. Fraunhofer began to make sets of achromatic doublets constantly experimenting and with the making of improved furnaces and annealing ovens produced a 7 inch optically perfect object glass in 1812. Guinand left in 1814. This and other lenses were ground and polished on machines designed by Liebherr, one of the partners in the instrument firm in Munich. Fraunhofer pioneered the use of Newton’s coloured rings to test the lens surfaces and designed other specialised instruments to check their accuracy. When measuring the refractive indices of different glasses for different coloured lights he discovered the two close yellow lines of the sodium spectrum. With low dispersions the two lines appeared as one and provided a reliable source of monochromatic light for measuring refractive indices. Following the discovery of the dark spectral lines (known as Fraunhofer lines), Fraunhofer together with Soldner made a list of the refractive indices of different glasses for different colours. With these advances in knowledge Fraunhofer was a world leader and manufactured and constructed some of the finest object glasses in the first quarter of the nineteenth century of exceptional quality. The telescope made for the Dorpat observatory in 1824 was 9.5 inches and was for many years the largest refractor in the world. With this telescope, measurements of 3,000 double stars were made whereas previously only 700 were known. The objective had a crown glass lens whose rear radius was shorter than the front radius of the succeeding flint. The two lenses were consequently separated by spacers at the edge which in small achromats is inconvenient. Unless this is done the main advantage of the Fraunhofer combination – aplanatism – is considerably impaired. This telescope now resides in the Deutches Museum in Munich and it is photographed on their web site. Fraunhofer made other important discoveries and inventions and was elected a member of the Munich Academy and knighted in 1826 just before he died at the young age of thirty-nine. He received a state funeral and was buried in Munich. For much of the above information I am indebted to The History of the Telescope by Henry C. King. The Fraunhofer telescope on offer here is strikingly similar to the Dorpat in construction. The wood mounting is modern. It has an objective doublet of 7 inches and must therefore have been one of the largest and finest telescopes in the world when it was constructed between 1812 and 1826. Note particularly the three spacers in the lens as mentioned in the Dorpat refractor above. (Only one - a silver rectangle - is visible in the photo of the lens at th top the other two are hidden by the lens mounting). It is signed Utzschneider und Fraunhofer in Müchen. The balance of the telescope is so perfect that - with the lens cap removed - it can be moved to any position with the lightest touch of the thumb and a single forefinger and stay stationary ‘hands off’, before locking the position and using the fine feed adjustments on the equatorial mount . No wonder Fraunhofer was lauded for his design and construction just as much as for his optics The equatorial mount is a little later than the telescope probably dating from around 1840 to 1850. Sale only by personal inspection at Monkton House (six miles from the centre of Edinburgh, Scotland, UK). This is a 'World Class' object even, (I hate to say it), a fantastic ‘furnishing piece’, but it is a very large item nearly two hundred years old and I am not prepared to take responsibility to try and describe every last dent and scratch etc. Like a fine second-hand vintage car it has to be seen and examined personally. I repeat a personal visit is the only way I am prepared to sell this telescope. Critically the buyer must examine the objective lens for himself in order to be satisfied with its condition as well as the rest of the instrument. What is truly wonderful about this object is the magnificent telescope tube and superb objective lens – I really do wonder if any other examples of this size exist outside a museum or institution and could conceivably come on to the market in the future. Unique is probably the most over-used word in the antiques business but this example may well be a ‘one-off’ opportunity to acquire one of these large historical instruments by possibly the most important of all early astronomical telescope manufacturers.


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