ASTRONOMICAL TELESCOPES PEASE 203 



liu<j^e telescopes were swiiii<^ from braced pole^s by tackle, and from 

 the pictures we judge that a sight through one of these monsters was 

 quite a social event. All lenses are subject to faults called aberra- 

 tions, and it was partly because of these and partly because of the 

 poor glass made in tho^e early days that astronomers had to make 

 use of this type of telescope. 



Newton, whose name is familiar to us all, believed that these 

 aberrations could not be removed, and consequently turned his at- 

 tention to mirrors. His first model was presented to the Royal 

 Society of London in 1GT2- Though this telescope itself has rented 

 idly on the shelves since that time, its spirit has moved in continu- 

 ously increasing waves through the Herschels, through Lord Rosse, 

 and through Common, culminating in the beautiful mechanism we 

 have in the 100-inch Hooker reflector on Mount Wilson. Newton's 

 mirror is made of a bronze called speculum, a heavy metal, very 

 brittle, which whenever it tarnishes must be polished anew in the 

 optical shop. 



Herschel, a musician at the English watering resort of Bath, made 

 many of these mirrors with his own hands, his largest telescope 

 having a mirror 4 feet in diameter and a tube 40 feet long. The 

 observer stood at the upper end and looked down into the tube, the 

 large mirror being tipped .so as to throw the image to one side. With 

 his telescopes Herschel discovered many nebulse, double stars, and 

 the planet Uranus. 



Zeal such as that of Herschel and his son, John, was also found in 

 the two great Irish gentlemen, Grubb and Lord Rosse. With no 

 other help than the workmen on his farm the latter accomplished a 

 prodigious amount of experimental work on metals, mirrors, and 

 methods of casting them. Telescope mountings of various sizes 

 culminated in his 6-foot reflector, with which he discovered that 

 many of the nebulae, of which Messier 51 is an example, are of a 

 spiral character, his drawing outlining the principal features por- 

 trayed in our photographs to-day. As a further indication of his 

 versatility, it may be mentioned that it was Lord Rosse who advised 

 the English Navy to protect its ships with armor plate. This inno 

 vation. however, like many others, was too early for the times. 



Meanwhile a way had been found to improve the lens, and Dolland 

 had made his achromatic objectives. Then Fraunhofer, a German 

 genius, having been taught how to make glass by the younger Gui- 

 nand, succeded in casting several fine pieces of glass and fashioning 

 them into a lens of very high precision, the curves for which he 

 calculated himself. We can picture Fraunhofer in his laboratory 

 making his disks of glass into prisms and lenses and tlien passing 

 the rays of the sun and a few of the brighter stars throuirh his 



