Thomas Romney Robinson was most impressed. "The sublime beauty can never be forgotten," he wrote, "by those fortunate enough to be present. Above, the sky, crowded with stars and illuminated by a most brilliant moon, seemed to look down auspiciously upon their work.
"Below, the furnaces poured out huge columns of nearly monochromatic yellow flame and the ignited crucibles during their passage through the air were fountains of red light, producing on the towers of the castle and the foliage of the trees such accidents of colour and shade as might almost transport fancy to the planets of a contrasted double star."
The director of Armagh Observatory, remembered by meteorologists as the inventor of the rotating-cup anemometer still used for measuring wind speed, was describing the casting in April 1842 in a special foundry set up for the purpose in the grounds of Birr Castle, Co Offaly, of the huge reflector for what was to be "the Leviathan of Parsonstown".
The giant telescope was the brain-child of the Earl of Rosse.
William Parsons, third Earl of Rosse, was born in June 1800. In his early years, he took an active part in politics but subsequently devoted himself entirely to astronomy.
Apart from its size, the earl's new telescope was unusual in being a reflecting telescope at a time when such instruments were thought to be inferior to the more traditional "refractors".
It had a 72-inch mirror weighing 4.5 tonnes and for over 70 years was the largest astronomical telescope in the world.
It took two more years to construct the tube of the instrument, which was then elevated in the gap between two walls over 50ft high built within the castle grounds.
With its enormous aperture, the telescope was able to gather more light than any other in existence and was thus able to look further into space than had ever been possible before.
It was brought into use in February 1845 and by April that year Rosse had made his most momentous astronomical discovery - that many of the galaxies possessed a spiral structure.
Only the direst exigencies of the Great Famine, during which he directed his energies to relief work and gave the major part of his rents to alleviate the poverty of his tenants, were allowed to interfere with Rosse's astronomical endeavours.
He continued an active and productive astronomer until the last year of his life, when he retired to Monkstown, Co Dublin, in the hope that the sea air might improve his failing health. He died there, 133 years ago today, on October 31st, 1867.