1-32 IIEttSCHEL ON COLOURED RING*. 



knife may be bruught over the first set, by which means the 

 fourth shadow will come upon the second set, and in this posi- 

 tion of the apparatus it will become visible. 

 4th. Lens on Tourtli Method, On a plain metalline mirror lay one slip 

 foraunc anan- °f o^ ass ' but w * tn a sina ^ piece of wood at duc end under it, 

 glewith metal, so that it may be kept about one tenth of an inch from the 

 mirror, and form an inclined plane. A 20-inch lens laid upon 

 the slip of glass will give three sets of rings. Two of them 

 will easily be seen; and when the shadow of the penknife is 

 held between them the third set will also be perceived. There 

 is but one shadow visible in this arrangement, which is the 

 third; the first and second shadows being lost in the bright 

 reflection from the mirror. 

 5th. A convex Fifth Method. I placed a 6|-inch double convex upon an 

 cavea^d^hpof ^"" icn double concave, and laid both together upon a plain 

 glass. slip of glass. This arrangement gave three sets of rings. They 



may be seen without the assistance of-shadows, by using only 

 pressure and tilting. The first had a black and the other twd 

 v had white centres. 



VI. Of four sets of Rings. 



Four sets of- The difficulty of seeing many sets of rings increases with 

 rin S s « their number, yet by a proper attention to the directions 



that are given four sets of concentric rings may be seen. 

 1st, Lens on a First Method. Let a slip of glass, with a 26-inch lens 

 glass forming (^j U p 0n j* fc e p] a ced upon a piece of looking glass. Un- 

 aa angle With . l to.,. ,, • ,. , t /> 



a mirror. der one end oi the slip, a small piece ot wood one tenth of 



an inch thick must be put, to keep it from touching the 

 looking glass. This arrangement will give us four sets of 

 rings. The first, third, and fourth may easily be seen, but 

 the second set will require some management. Of the three 

 shadows, which this apparatus gives, -the second and third 

 must be brought between the first and fourth sets of rings, 

 in which situation the second set of rings wjjl become visible. 

 2d. Piano cor.- Second Method. When three slips of glass are laid upon 

 rex 'ens on a metalline mirror, and a plano-convex lens of about 17 



three sii,js Of i , ' . 



glass & metal, inches focus is placed with its convex siue upon them, four 

 sets of rings may be seen ; but this experiment requires a 

 very bright day, and very clean, highly polished slips of 



plain 



