786 



PLATE XXIX. 



Fig. 418. If A B and AC represent tlie comparative 

 velocity of light and of the eartli, in their respective 

 directions, a telescope must be placed in the direction 

 BC, in order to see the star D, and the star v^ill ap- 

 pear at E. P. 437. 



Fig. 419. The spectrum produced by lookingthrough 

 a prism at a narrow line of light. P. 438. 



Fig. 420. The appearance of a portion of the blue 

 light at the bottom of a candle, viewed through a 

 prism. P. 438. 



Fig. 421. The appearance of a circular aperture, 

 moderately large, when viewed through a prism. P. 

 439. 



Fig. 422. A B and C D represent the appearance of 

 the two ends of a broad white surface, or a window, 

 'when viewed through a prism. The oblique stripes of 

 colour show the degrees by which the lights of different 

 kinds enter into the compound light. It follows from 

 this analysis, that the colours, horizontally opposite 

 each other in A B and C D, would always together 

 make up white light. P. 439. 



Fig. 423. The colours on the circle A exhibit, when 

 whirled swiftly round, a whitish light resembling B. 

 P. 440. 



Fig. 424 . . 426. The colours of the circle A pro- 

 duce, when made to revolve rapidly, the tints shown 

 atB. P. 440. 



Fig. 427. A triangular figure, exhibiting in theory 

 all possible shades of colours. The red, the green, and 

 the violet, are single at their respective angles, and are 

 gradually shaded off towards the opposite sides: a 

 little yellow and blue only are added in their places, 

 in order to supply the want of brilliancy in the colours 



which ought to compose them. The centre is grey, atvd 

 the lights of any two colours, which are found at equal 

 distaiices on opposite sides of it, would always very 

 nearly make up together white light, as yellow and 

 violet, greenish blue and red, or blue and orange. P. 

 441. 



Fig. 428. The appearance of a pin, and of the word 

 POKER, when viewed by looking along the surface of a 

 red hot poker. From Dr. WoUaston. P. 442. 



Fig. 429. The appearance of an oblique line, and of 

 the word spin it, viewed simply through rectified spi- 

 rit of wine, and through a portion of the spirit mixing 

 by degrees with the water on which it floats. From 

 Dr. WoUaston. P. 442. 



Fig. 430. The colours of the primary and secondary 

 rainbow, as they usually appear. P. 443. ! 



Fig. 431. The most common form of halos and 

 parhelia. P. 444. 



Fig. 432. Magnified figures of the simplest crystals 

 of snow, which are sufficient to account for the produc- 

 tion of halos. From Nettis. P. 444. 



Fig. 433. A complicated system of halos. From 

 Lowitz. The arcs A, B, and C, were coloured, and, 

 like all the other coloured parts, bad the red towards 

 the sun. D and E are two anthelia. P. 444. 



Fig. 434. The figures of two complicated flakes of 

 snow. From Nettis. P. 444. 



Fig. 435. The ray of light AB, falling perpendicu- 

 larly on the surface of the piece of calcarious spar C D 

 atB, is divided into the portions BE and BF: the 

 portion B E passing to the point E, where the surface 

 of the spheroid EGH, inscribed in the greater angle 

 of the crystal, becomes parallel to C B. P. 44d. 



