The great telescope at Birr Castle, Ireland, built by Lord Rosse and put into service in 1845. The primary mirror is 72 inches in diameter. However, due to difficulties in measuring and optimizing the figure of the mirror and in mounting it so it did not distort, the images were mediocre. In addition, as can be gathered from this picture, it was difficult to get it to track smoothly and it could only follow sources for a limited time as they passed the meridian (north-south line passing directly overhead). (photo by G. Rieke)
	Lord Rosse used the telescope to discover the spiral structure of galaxies - which then became known as "spiral nebulae." Here is his drawing of M33. At the time, photography was in its infancy and no photographic plates were available with the sensitivity to use in astronomy, so the measurements were all made by eye and hand drawn. (photo by G. Rieke)
	For comparison, here is Hubble's plate of M33, published in 1926. In the 80 years since the construction of Lord Rosse's telescope, the mirror size had hardly grown (72 to 100 inches). The improvements came about from: 1.) better telescope optics to make sharper images; 2.) telescopes that tracked smoothly for long times; and 3.) photographic plates that could take advantage of the first two improvements with long, sensitive exposures.