Mr. H. Taylor on an Optical Illusion. 345 



The dried residue of No. I. yielded 4800 per cent, of ash. 



LIII. On the Apparent Motion of the Figures in certain Pat- 

 terns of Blue and Red Worsted. By Henry Taylor, Esq. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, Guildford, Oct. 12, 1848. 



THE apparent motion of the figures in certain patterns of 

 blue and red worsted is sufficiently well-known to have 

 excited some attention among the learned as well as the un- 

 learned, but, so far as I know, without receiving any satisfac- 

 tory explanation. After having examined the subject for some 

 time, I believe I have succeeded in making out the cause of 

 this singular phaenomenon ; and if the following observations 

 are deemed of sufficient importance, I should be glad to have 

 them inserted in the pages of your Journal. 



If certain patterns of blue and red worsted-work are ex- 

 amined by candle-light, it is found that when they are moved 

 about, the figures have a tremulous appearance as if they were 

 moving faster than the ground of the pattern — and blue and 

 red are the only colours exhibiting this remarkable property 

 — although it must be observed that some persons are so con- 

 stituted as not to perceive the illusion under any circum- 

 stances. 



Phil. Mag. S. 3. Vol. 33. No. 223. Nov. 1848. 2 A 



