310 



SCIENTIFIC AMUSEMENTS. 



viewed is placed between the two reflecting surfaces (fig. 151). The 

 effect of this is that an eye properly situated in front receives a 



number of impressions arising from 

 the formation of a number of 

 virtual images which are arranged 

 symmetrically around the line 

 where the surfaces of the two 

 mirrors intersect ; so that if the 

 mirrors are inclined at an angle of 

 60, there will be 5 images visible 

 besides the real object, all 6 being 

 arranged like a 6-pointed star 



radiating out from a common cen- 

 Fig. 151. Kaleidoscope. tral point< If the angle of the 



mirrors be 45, then 7 images will be seen as well as the real 



object, forming an 8-fold 

 star.* A variety of opti- 

 cal toys producing geo- 

 metrical patterns on this 

 principle are sold ; one 

 of the oldest forms of ka- 

 leidoscope (from the 

 Greek signifying " ren- 

 dering visible of beautiful 

 forms ") consists of a paste- 

 board or metal tube with 

 two mirrors arranged at 

 an angle of 60, so that 

 the vertical section of the 

 whole is like fig. 152. 

 Fig. 153 represents a hori- 

 zontal section across the 



Fig. 153. Kaleido- 

 scope. 



line mn. At the far end 

 is a round glass plate, a, 

 and over this a cap, cc, 

 with a glass end, the space 

 between the two glass 

 plates containing beads, coloured bits of glass, &c. This cap 



Fig. 152. Kaleido- 

 scope. 



* The rule guiding the number of images is that, if the angle between the 



1 ^fiO 



mirrors is - of 4 right angles, or - > then an w-rayed star shape will be 



formed, one ray being the real object and the others virtual images. With 

 an angle of 30 a 12-rayed star would consequently be formed, with 40 a 

 9-rayed star, and so on. 



