NATURAL PHILOSOPHY. 155 



moted the advancement of science. Up to a recent period, the flint 

 o-lass for achromatic telescopes was entirely of foreign manufacture. 

 Since the reduction in the duty, great improvements have been made 

 in this department. The making of the large flint glass was intrusted 

 to Mr. Chance, of Birmingham, who at first hesitated to manufacture 

 one larger than 9 inches in diameter. On being urged, however, 

 by Mr. Craig, he succeeded in producing one of 24 inches ; perfectly 

 clear, and homogeneous in structure. Besides this, there is a second 

 of plate glass of the same dimensions, cast by the Thames Plate Glass 

 Companv. The tube rests upon a light wooden framework, with iron 

 wheels attached, and is fitted to a circular iron railway at a distance 

 of 52 feet from the centre of the tower. The chain by which it is 

 lowered is capable of sustaining a weight of 13 tons, though the 

 weight of the tube is only 3. Notwithstanding the immense size of 



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the instrument, the machinery is such that it can move either in azi- 

 muth, or up to an altitude of 80, with as much ease and rapidity as 

 an ordinary telescope, and, from the nature of the mechanical arrange- 

 ments, with far greater certainty as to results. The slightest force 

 applied to the wheel on the iron rail, causes the instrument to move 

 horizontally round the central tower, while a wheel at the right hand 

 of the observer enables him to elevate or depress the object-glass with 

 the greatest precision and facility. With respect to the magnifying 

 power of this novel instrument, it is only necessary to state that, 

 though the focus is not so sharp as it will be shortly, it has already 

 separated the nebulas in the same way as Lord Rosse's. It has also 

 separated some of the double stars in the Great Bear, and shown dis- 

 tinctly a clear distance of 50 or 60 between them, with several 

 other stars occupying the intervening space. Ordinary readers will 

 better understand the extraordinasy magnifying power of the tele- 

 scope, when we inform them that by it a quarter-inch letter can be 

 read at the distance of half a mile. 



The London Observer furnishes the following additional particulars 

 relative to the power of this new instrument ; it says : "It has been 

 already ascertained, that, as a measuring instrument, or for penetrat- 

 ing space, its powers are unapproachable by all other instruments. It 

 separates minute points of light so distinctly, that its qualifications as 

 a discovering telescope must be extremely valuable. It resolves the 

 milky way, not simply into beautiful and brilliant star-dust, to use the 

 language of astronomers, but subdivides this ' dust ' into regular 

 constellations, showing counterparts of the Orion, the Great Bear, 

 and the other brilliant galaxies of our system, adorned, in addition, 

 with the most varied and gorgeous colors. The lenses are so perfectly 

 achromatic, that the planet Saturn appears of milk-like whiteness ; 

 and, as regards this planet, a good deal of scientific interest has been 

 recently attached to it, in consequence of the distinguished American 

 astronomer, Bond, of the Cambridge Observatory, Massachusetts, 

 having stated he believed he saw a third ring or belt round the planet. 

 Professor Challis brought the Northumberland telescope at Cambridge 

 to bear upon it, but failed in discovering it. Lord Rosse's gigantic 

 14* 



