116 The Earl of Rosse's Telescopes, and their 



and as 2-12 to 1, as to the capability of penetrating 

 space, or detecting nebulous or sidereal objects at the ex- 

 treme distance of visibility. Hence, whilst the range of 

 telescopic vision in a refractor of two feet aperture would 

 embrace a sphere in space represented by a diameter of 2 ; 

 the six-feet speculum (assuming both instruments to be of 

 equal optical perfection, magnifying equally, and allowing 

 fifty per cent, for loss of light for two reflections in the 

 one case, and none (?) in the other) would comprehend a 

 sphere of about 4*24 diameter, — the outer shell of which, 

 1*12 in thickness, being the province, of the great instrument 

 alone. But let us reduce these proportions to sections of 

 equal spaces, that we may judge more accurately of the rela- 

 tive powers. Now, the solid contents of different spheres, 

 we know, are in the ratio of the cubes of their diameters. 

 Hence the comparative spheres, penetrated by the two in- 

 struments referred to, should be as 4*24 3 to 2 3 ; that is, as 

 9*5 to 1. Deducting, then, from this vast grasp of space the 

 inner sphere, capable of being explored by other instruments, 

 we find that, out of nearly ten sections of space reached by 

 this telescope, there are nearly nine sections which the six- 

 feet speculum may embrace as peculiarly its own ! 



What its revelations yet may prove, then, we can have no 

 idea. Several thousands of nebulae have been catalogued : 

 the great reflector might add to these tens of thousands more. 

 But this, seeing how few nights in a year are favourable for 

 the highest powers, must be the work of years of perseve- 

 rance. It would be a worthy undertaking for the Government 

 of a great country, to afford the means of multiplying such 

 gigantic instruments. Application is to be made, in this di- 

 rection, for a six-feet reflector at the Cape of Good Hope, 

 for the examination of the heavens towards the southern pole. 

 Lord Rosse, with his usual nobleness of liberality, will yield 

 up his laboratory, machinery, and men, to the service of Go- 

 vernment, and is willing, moreover, to give the direction and 

 guidance of his master-mind. Will the British nation be con- 

 tent with a refusal \ 



The range opened out to us by the great telescope at Birr 

 Casllc. is best, perhaps, apprehended by the now usual mea- 



