Curiosities of Science. 95 



was 12f or 13 inches, so that " it collected the sun's rays at 

 the distance of 6 inches." The rays reflected by the specu- 

 lum were received upon a plane metallic speculum inclined 45 

 to the axis of the tube, so as to reflect them to the side of the 

 tube in which there was an aperture to receive a small tube 

 with a plano-convex eye-glass whose radius was one-twelfth 

 of an inch, by means of which the image formed by the specu- 

 lum was magnified 38 times. Such was the first reflecting 

 telescope applied to the heavens ; but Sir David Brewster de- 

 scribes this instrument as small and ill-made ; and fifty years 

 elapsed before telescopes of the Newtonian form became useful 

 in astronomy. 



SIR WILLIAM HEESCHEL'S GREAT TELESCOPE AT SLOUGH. 



The plan of this Telescope was intimated by Herschel, 

 through Sir Joseph Banks, to George III., who offered to de- 

 fray the whole expense of it ; a noble act of liberality, which 

 has never been imitated by any other British sovereign. Towards 

 the close of 1785, accordingly, Herschel began to construct his 

 reflecting telescope, forty feet in length, and having a speculum 

 fully four feet in diameter. The thickness of the speculum, 

 which was uniform in every part, was 3 2 inches, and its weight 

 nearly 2118 pounds ; the metal being composed of 32 copper, 

 and 1O7 of tin : it was the third speculum cast, the two pre- 

 vious attempts having failed. The speculum, when not in use, 

 was preserved from damp by a tin cover, fitted upon a rim of 

 close-grained cloth. The tube of the telescope was 39 ft. 4 in. 

 long, and its width 4 ft. 10 in. ; it was made of iron, and was 

 3000 Ibs. lighter than if it had been made of wood. The ob- 

 server was seated in a suspended movable seat at the mouth 

 of the tube, and viewed the image of the object with a magni- 

 fying lens or eye-piece. The focus of the speculum, or place 

 of the image, was within four inches of the lower side of the 

 mouth of the tube, and came forward into the air, so that there 

 was space for part of the head above the eye, to prevent it 

 from intercepting many of the rays going from the object to 

 the mirror. The eye-piece moved in a tube carried by a slider 

 directed to the centre of the speculum, and fixed on an ad- 

 justible foundation at the mouth of the tube. It was com- 

 pleted on the 27th August 1789; and the very first moment it 

 was directed to the heavens, a new body was added to the 

 solar system, namely, Saturn and six of its satellites ; and in 

 less than a month after, the seventh satellite of Saturn, " an 

 object," says Sir John Herschel, "of a far higher order of 

 difficulty." Abridged from the North-British Itevieu;No. 3. 



This magnificent instrument stood on the lawn in the rear of Sir 

 William Herschel' a house at Slough ; and some of our readers, like our- 



