&{u dT0ttibpb.ce. 



THE GREAT ROSSE TELESCOPE. 



The originator and architect of this magnificent instrument had long 

 been distinguished in scientific research as Lord Oxmantown ; and may 

 be considered to have gracefully commemorated his succession to the 

 Earldom of Rosse, and his Presidency of the Royal Society, by the com- 

 pletion of this marvellous work, with which his name will be hereafter 

 indissolubly associated. 



The Great Reflecting Telescope at Birr Castle (of which the Fron- 

 tispiece represents a portion*) will be found fully described at pp. 96-99 

 of the present volume of Curiosities of Science. 



This matchless instrument has already disclosed "forms of stellar 

 arrangement indicating modes of dynamic action never before contem- 

 plated in celestial mechanics." "In these departments of research, 

 the examination of the configurations of nebulae, and the resolution of 

 nebulae into stars (says the Rev. Dr. Scoresby), the six-feet speculum 

 has had its grandest triumphs, and the noble artificer and observer the 

 highest rewards of his talents and enterprise. Altogether, the quan- 

 tity of work done during a peiiod of about seven years including a 

 winter when a noble philanthropy for a starving population absorbed the 

 keenest interests of science has been decidedly great ; and the new- 

 knowledge acquired concerning the handiwork of the great Creator 

 amply satisfying of even sanguine expectation." 



SIR HUMPHRY DAVY'S OWN MODEL OF HIS SAFETY-LAMP. 



Of the several contrivances which have been proposed for safely light- 

 ing coal-mines subject to the visitation of fire damp, or carburetted 

 hydrogen, the Safety- Lamp of Sir Humphry Davy is the only one which 

 has ever been judged safe, and been extensively employed. The in- 

 ventor first turned his attention to the subject in 1815, when Davy 

 began a minute chemical examination of fire-damp, and found that it 

 required an admixture of a large quantity of atmosphei'ic air to render 

 it explosive. He then ascertained that explosions of inflammable gases 

 were incapable of being passed through long narrow metallic tubes, 

 and that this principle of security was still obtained by dimiiiishing 

 their length and increasing their number. This fact led to trials upon 

 sieves made of wire-gauze ; when Davy found that if a piece of wire- 

 gauze was held over the flame of a lamp, or of coal-gas, it prevented 

 the flame from passing ; and he ascertained that a flame confined in a 

 cylinder of very fine wire-gauze did not explode even in a mixture of 

 oxygen and hydrogen, but that the gases burnt in it with great vivacity. 



These experiments served as the basis of the Safety-Lamp. The 

 apertures in the gauze, Davy tells us in his work on the subject, should 

 not be more than ^d of an inch square. The lamp is screwed on to 

 the bottom of the wire-gauze cylinder. When it is lighted, and gradu- 

 ally introduced into an atmosphere mixed with fire-damp, the size and 

 length of the flame are first increased. When the inflammable gas forms 

 as much as T \th of the volume of air, the cylinder becomes filled with a 

 feeble blue flame, within which the flame of the wick burns brightly, and 

 the light of the wick continues till the fire-damp increases to ith or -J-th ; 



* From a photograph, with figures, to show the relative size of the tube aperture . 



