Parsons, William

William Parsons, Third Earl of Rosse (1800-1867)

One of the main problems of astronomy in the early nineteenth century was that of the status of the sun and the galaxy containing it. The problem could not be resolved without a far more powerful telescope than available at the time. In the 1840s, Parsons designed a reflecting telescope with a mirror 72 inches (1.83 m) in diameter, which was then, and for the next 70 years, the largest in the world. This engineering feat was considerable, as Parsons had to design and make everything himself. He set up a foundry to cast the mirror, and invented a huge machine to polish it.

His telescope was able to gather more light and hence see further into space than had been possible before. It was able to show the galaxies in detail, and this resulted in the Earl's most fundamental discovery - that many of the galaxies are spiral in shape. He published accounts of all his discoveries and freely shared his knowledge with all those who came from all over Europe, America and Australia to observe at Birr.

During his life he received many distinctions, including being President of the Royal Society and Chancellor of the University of Dublin. Two of his sons, Laurence and Charles, are renowned in their own right.

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