Alcohol and its Compounds. 41 



2nd, O H 4 + oxide of binolefiant gas. 

 C 4 H 4 + 2 aldehyde. 

 C 4 H 4 + 3 aldehydic acid. 

 C 4 H 4 + 4 hydrous acetic acid. 



Article IV. 



On the Action of Flashes of Light upon rapidly Rotating 

 Disks. By Charles Tomlinson, Esq. 



Professor Wheatstone, I believe, first announced the 

 beautiful fact " that a rapidly moving wheel, or a revolving 

 disk on which any object is painted, seems perfectly sta- 

 tionary when illuminated by the explosion of the electric 

 jar." 



This experiment is adduced by Mr. Wheatstone, to shew 

 that the duration of electric light embraces a point of time 

 so extremely minute that the revolving wheel, or disk, has 

 not time to pass through any perceptible space, and that, 

 therefore, it appears, during the illumination, stationary ; 

 I find, however, that the effect is not confined to electricity, 

 but may be produced by any very sudden flash of light. 



Of the disks that I employed I need only mention two : 

 The first, six inches in diameter, was divided into sixteen 

 parts, painted, alternately, red and black ; on the second 

 disk, of the same size, were painted in large characters the 

 words, AT REST, on white ground. Both disks were 

 connected with a small multiplying arrangement. 



The effects can be produced with phosphuretted hydrogen, 

 exhibited in bubbles from phosphuret of lime, in water. 

 When the bubbles come up slowly without interrupting 

 each other, both disks appear stationary during rotation ; 

 but when the bubbles come up too quickly, the black and 

 red spaces exhibit a dancing sort of motion, and sometimes 

 two black spaces seem joined into one, to the exclusion of 

 the intervening red, and vice versa ; so also with the 

 second disk, the words cross each other in various directions 

 when the flashes of light interfere with each other; and, in 

 both cases, confusion is, of course, excited when an impres- 

 sion is made on the retina before succeeding impressions 

 have departed. Similar confused effects are produced with 



