156 ANNUAL OF SCIENTIFIC DISCOVERY. 



telescope was also employed upon it In vain ; and it became a matter 

 of great interest to the astronomical world, to ascertain whether there 

 was a third ring or not ; and this question has been solved by the 

 Craig telescope ; the third ring, of a clear, brilliant gray color, having 

 been distinctly seen. This is owing to the great quantity of light 

 which the Wandsworth telescope brings to the eye of the observer 

 from this planet, giving a bright appearance to what, in an instrument 

 of less power, would have been completely invisible. 



" Some idea of its powers may be formed from the fact, that it mag- 

 nifies the light of the moon 40,000 times ; and in coarse objects, like 

 the outlines of the lunar mountains and the craters, the whole of these 

 rays may be allowed to pass at once to the focal point, as they do not 

 in such objects confuse it in any appreciable degree. In the Craig 

 telescope, the moon is a most magnificent object, and perfectly color- 

 less, enabling the beholder to trace the outlines of the various 

 mountain ranges with such vivid distinctness as to make us long for 

 fine clear weather, in order to bring the whole powers of this marvel- 

 lous instrument upon our satellite. It is positively asserted that of a 

 favorable evening, if there was a building or object of the size of 

 Westminster Abbey in the moon, the whole of its parts and propor- 

 tions would be distinctly revealed. As an illustration of its space-pen- 

 etrating powers, and the manner in which it grasps in the light, it may 

 be stated, that soon after it was erected it was directed to a test object. 

 a minute speck of light in one of the constellations, which is not to be 

 seen at all times by the most excellent instruments, though guided by 

 first rate observers, and in profound darkness. The Craig telescope 

 at once discovered that this test object was not a minute speck of 

 light, but a brilliant double star. As soon as it is finally adjusted, Mr. 

 Craig proposes to direct the instrument to the planet Venus, to exam- 

 ine it minutely, in the hope that he may be able to settle the question 

 of whether she has a satellite or not. We need not say what an 

 advantage the solution of this fact would be to science. 



" But wonderful as are the effects of this telescope, it is not yet 

 perfect, and it has been found that a part of one of the lenses is too 

 ilat by about the five-thousandth part of an inch ! To many it may 

 appear incredible that the five-thousandth part of an inch can be 

 estimable so as to be appreciable and measured; but the indistinct- 

 ness of a portion of the image revealed the fact. The rays of light 

 which fall upon that part of the lens go beyond the focal length, and 

 render the object indistinct, and confuse the image. This portion of 

 the lens has to be " stopped out " when extraordinary accuracy of 

 definition is required ; as, for instance, in observing so fine a point 

 as the third ring of Saturn ; and, as the aperture is so large, the 

 absence of this small portion of the rays is not important, the quan- 

 tity of light being so great. It was at first feared that the attempt to 

 correct this defect might produce the inconvenience of over correct- 

 ing it, and produce an error on the other side ; but Mr. Gravatt has 

 devised a plan by which the lens, which was polished in the first 

 instance by four workmen, may now be repolished by machinery upon 



