xl 



though of course too thin for use. This he regarded as a valuable result, 

 for it sho\Yed the possibility of going far beyond the six feet, should such 

 optical power ever be required. In these disasters his unfailing good 

 temper and patience were not less admirable than his exhaustless mecha- 

 nical talent. The whole mighty instrument was so far complete by Fe- 

 bruary 1845, that on the 13th of that month he, his friend the late Sir 

 James South, and another, saw in a lucid interval of clouds a few double 

 stars and clusters. 



Lord Rosse has given in the paper just referred to (1861) ample details 

 of the telescope, both in respect of casting and figuring the specula and of 

 the mechanism by which it is pointed to the heavens, and the observers 

 enabled to use it with convenience and safety. In these we need not fol- 

 low him beyond noticing the modest and undemonstrative character of the 

 description, which gives but a very faint idea of the magnificence of what 

 he had achieved. To those of us who have seen the telescope, and still 

 more to the few who were present at the casting and polishing of the 

 specula, it is but a lifeless shadow. They can never forget the machinery 

 and furnaces that were installed in the towers and courts of the old castle 

 whose walls still show traces of the sieges sustained in times of yore> 

 the intelligence and discipline of the workmen whom he had formed from 

 ignorant Irish labourers, and above all the matchless self-possession and 

 unfailing resources of the master mind that guided all. In even beholding 

 the instrument it is not easy to realize its colossal vastness ; the machinery 

 which moves it disappoints by its excessive simplicity, and it is not till one 

 stands in the highest observing gallery and looks into the profound below, 

 or over the surrounding country, that he obtains a true measure of its 

 magnitude, and feels that it is sublime. It deserves notice that all this 

 massive work was executed in Lord Rosse's laboratory, and that the whole 

 had been so thoroughly considered that in no instance was it found neces- 

 sary to deviate from the drawings which had been prepared. 



With respect to its optical power, little need be added to what is said in 

 the memoir of 1 861. A more unfavourable location for it could hardly be 

 found than the vicinity of the Bog of Allen ; and its performance gives 

 little earnest of what it could do in a finer climate and a few thousand feet 

 above the sea. Hitherto it has also suffered from a disturbing cause pecu- 

 liar to reflectors, and increasing very rapidly with their bulk. Besides the 

 undulations of the air through which they look (which affect all tele- 

 scopes), they have air-currents in their tubes caused by the great speculum 

 being warmer than the atmosphere. The air in contact with the metal is 

 heated, and rises along the upper side of the tube, while a stream of cold 

 air replaces it, descending on the lower ; and the eddies of the two cause 

 strange wings and twirlings in the image. This goes on increasing as the 

 night becomes colder, till sometimes all definition is lost. An example of 

 this was given on March 5, 1845. The speculum was uncovered while 

 cooler than the air, and was, of course, dewed. This did not dry off till 



