D. Gill, Lord Rosse, W. de la Rue 169 



reflecting telescopes during the nineteenth century was 

 entirely the work of amateurs. William Parsons, third Earl 

 of Rosse (1800-1867), took the first step in 1827. As William 

 Herschel had never published his methods, there was no 

 established procedure to shape concave mirrors. Lord Rosse 

 had to start from the beginning, and to invent the machine 

 for grinding and polishing the speculum metal to the required 

 shape. After a number of attempts he was eminently 

 successful, and in 1845 completed a mirror six feet in dia- 

 meter with a focal length of nearly sixty feet. The structure 

 necessary to hold and move such a gigantic telescope pre- 

 sented considerable engineering difficulties, but these were 

 overcome, with the result that Lord Rosse was soon able 

 to announce a number of important discoveries. Many 

 luminosities that had been classed as nebulae were found to 

 consist of closely packed star clusters. Others remained 

 unresolved, and among them the interesting family of spiral 

 nebulae was recorded. Further improvements in the methods 

 of shaping and polishing mirrors are due to William Lassell 

 (1799-1880) and James Nasmyth (1808-1890). The former, 

 a Lancashire brewer, had already, in 1820, constructed a 

 small telescope with his own hands, being too poor to 

 purchase one. Later he improved on Lord Rosse's methods, 

 and with a larger instrument discovered two new satellites 

 of Uranus, a satellite of Neptune, and an eighth satellite of 

 Saturn. James Nasmyth, chiefly known as the inventor of 

 the steam hammer, was also much interested in astronomy. 

 The sharpness of his vision and quality of his instrument 

 is shown by his observations of the granular structure of the 

 solar surface which no one had noticed before him. 



Warren de la Rue (1815-1889), a member of the well- 

 known printing firm, was a generous supporter of many 

 scientific enterprises. In early life he had made further 

 improvements in the process of shaping concave mirrors, 

 and successfully constructed a reflecting telescope. He was 

 the first to appreciate the opportunities offered to astronomers 

 by the invention of photography, and in 1860 fitted out an 

 expedition to observe a total eclipse in Spain. The slow 

 acting plates of the time were not sufficiently sensitive to 

 show the solar corona which appears during an eclipse, but 



