214 



Mr. G. J. Burch. On the Relation of 



between the objective of A and the objective of a second telescope 

 C, magnifying five times. The first telescope A being inverted, 

 diminishes the image to one-tenth of its size, and the second tele- 

 scope only magnifies it five times, so that it appears to the eye 

 half the size it would without the telescopes, and correspondingly 

 brighter. Although the two telescopes were merely supported by 



retort stands and roughly adjusted, the definition was quite good 

 enough and the light strong enough to show the complementary 

 spectrum extremely well. 



But the white light used was merely that reflected from card, and 

 was in consequence weak in the extreme violet rays. By the following 

 arrangement white light reflected from a mirror may be employed : — 

 The disc A, figs. 7, 8, which is 25 cms. in diameter, has two sectors of 

 30° aperture, and reaching within 2 cms. of the centre, cut away at 

 opposite ends of a diameter. The disc B, 15 cms. in diameter, has two 

 narrow slits of about 1° or 2° aperture and 180° apart. Both discs are 

 blacked and mounted upon the same shaft, which is furnished with a 

 nut and broad washer, so that they can be clamped together. The 



